Where's the "it depends" option?
Really comes down to if it was unplanned / uncontrolled and if it could of potentially put a person's safety at risk?
Was it a 3L bottle of juice or was it a 1T pallet?
Was it within a designated loading zone (and thus access around the truck is prevented) or on the side of the road?
Was it while the truck was moving or stationary?

The item was a metal fuel pump. WorkSafe have said no.

That would be within their guidelines, it would become notifiable if it was an item that exposed workers in the immediate vicinity to risk of injury or illness ie drum of chemicals, gas bottle etc;
https://www.worksafe.govt.nz/notifications/notifiable-event/what-is-a-notifiable-event/

The item was a metal fuel pump. WorkSafe have said no. — Michael Wilson

What questions did WorkSafe ask you, relating to the event?
Just curious because I don't think I have ever gotten a straight answer to a question from WorkSafe, mostly it's a reciting of the section of the act and then "you need to decide..."

None. I just got an email back saying that they did not consider it reportable.

totally agree with your statement about their response, sometimes not very helpful especially when you are asking for guidance or clarification.

We have had 2 fall from height incidents (railings hit by vehicles and dislodgeed), we notified on both occasions. Worksafe agreed one was notifiable, but said the other one was not. When I queried the difference, the explanation I was given was that for one incident a pedestrian was in the vicinity and therefore could have been severly injured/killed, whereas in the other one, there was no pedestrians, not over a walkway so much lower risk.

Would it not be considered an insecure load so come under the land transport act, so would not be reportable to worksafe

Would it not be considered an insecure load so come under the land transport act, so would not be reportable to worksafe — Don Ramsay

It's the old "all depends" Don, as Matt pointed out in his post, where the truck was (public road vs private loading zone), was it stationary and being unloaded, hurtling down State Highway 1 at full cry.

And judging by this RNZ report WorkSafe: 'Our task is bigger than our available resources' regardless of which agency has jurisdiction, lack of cash may see it slip through the cracks.

SteveH

Having been involved in an incident that occurred in a yard but due to the legal determination was classed as a road, Worksafe was not interested but the police did pursue a prosecution of the driver. So it is the location of the incident that is foremost when it comes to transport-related events so possibly it would be a case of a chain of responsibility issue so the security of the load would be in question??

Would it not be considered an insecure load so come under the land transport act, so would not be reportable to worksafe — Don Ramsay

Again it would potentially depend on if the incident happened during road transport (or after it was considered secured for transport) or during loading/unloading. It looks like there is a offense in the Land Transport act for failing to secure a load (and strict liability if you do fail to), but there seems to be no obligation in the act to specifically report a lost load to the regulator (NZTA or applicable RCA) so unless caught red handed you could get away with it.
But given that the one of reasons for the insecure load offence must be to reduce the occurances of people being exposed to a the risk of serious injury from insecure loads falling of vehicles then would an item falling from a vehicle while being transported not have to be consider notifiable if it were to occur???

If in doubt - Fill the form out.

Nobody has ever gotten into trouble for over reporting events. .

If in doubt - Fill the form out.

Nobody has ever gotten into trouble for over reporting — Chris Hyndman

In the first few months of HSWA I remember reporting a potential notifiable incident to WorkSafe where the person on the phone seems a little puzzled as to why I was reporting it (as in this ain't a serious harm injury...) but that was basically my answer "I don't know if it is or isn't, but there a fine for not reporting but no fine for (reasonably) bothering WorkSafe... so hence the call"

We work a lot on whether or not someone was in the drop zone - or will dropping a conductor affect public safety

We don't generally consider items falling from trucks as notifiable falling from height

This is my take when deciding what is a notifiable event and what is not; as we know, Notifiable Incidents are covered by Sec 24 HSWA 2015. This section has 13 events, that if were to eventuate, would be considered a notifiable event.
The question asked is: “If something falls off a Truck, does this count as a fall from height?”. As per sec 24, the event is:
A FALL FROM HEIGHT OF ANY PLANT, SUBSTANCE OR THING.
For this incident (or any similar event) to be notifiable, there must be context; otherwise, the above sentence would mean anything, anywhere at any time that falls is notifiable!

To counter this, legislation is written with qualifiers; as in - if ‘this’ happens, then ‘that’ must happen
The qualifier is the first paragraph in Sec 24
A notifiable incident is an unplanned or uncontrolled incident in relation to a workplace that exposes the health and safety of workers or others to a serious risk arising from immediate or imminent exposure to:
Then is the list of 13 specific events.

For one of the 13 events to be notifiable, the first paragraph must apply (or be true).

Qualifying paragraphs are made up of elements, and for the qualifier to apply (to be true), all elements MUST be met. The absence of just one element renders the qualifier redundant.
What I consider to be the elements from the qualifying paragraph are:
• unplanned or uncontrolled
• relation to a workplace
• exposes the health and safety of workers or others
• serious risk
• immediate or imminent exposure

In an attempt to explain, I have added a True or False (with assumptions) to each element from the question:
• unplanned or uncontrolled: TRUE – the metal fuel pump was not meant to fall
• relation to a workplace: TRUE – it happened at work (assumption here)
• exposes the health and safety of workers or others: I assume FALSE, but not enough information is provided to be certain
• serious risk others: I assume FALSE, but not enough information is provided to be certain
• immediate or imminent exposure others: I assume FALSE, but not enough information is provided to be certain

Considering my assumptions, the qualifier is rendered redundant on up to three elements, making the remaining part of the regulation redundant, meaning it is not notifiable. If there is no qualifier, nearly every incident that happens at work is notifiable.

Finally, I am all for notifying WorkSafe, but always consider this: once you notify, you can’t un-notify. Once notified, the event/incident becomes part of the WorkSafe system which you are no longer in control of.

immediate or imminent exposure — Robb

This is the one part that I see most used to "justify" not reporting - "yeah we dropped a tonne of scaffold poles off the hiab, but no one was walking past at the time so it's not notifiable"...
While I will accept that satisfies the immediate exposure part I would say unless there was measures in place to prevent people being in the drop zone (e.g. taped off) then there would have still been a risk of imminent exposure. I would also argue that if the area was taped of to prevent people being in the drop zone the event should be considered to have been a controlled incident with respect to any person's safety and so would fail the test for being notifiable on multiple points.

still been a risk of imminent exposure — MattD2

I agree with this 100%. Without getting into a debate about the legislation being written correctly or not, the decision to notify or not cannot include "still been a risk of imminent exposure". Otherwise and again, nearly all events on site would be notifiable.
We have to stick to what is required by legislation, that being: there is imminent exposure, or there is not imminent exposure.

nearly all events on site would be notifiable. — Robb

Or none of them are (unless it was so close that it actual did seriously hurt someone... but then it would like just be a notifiable injury).

Not really sure if "Is this notifiable" is the right question.
Is it significant? Yes
Are there learnings we could take from the event? Yes
We would need additional background fact for context as the question you pose does not contain sufficient evidence to arrive at the answer you are seeking.
Your answers to questions appear incomplete also.
Was it the fuel pump of the stationary truck while the vehicle was being serviced in the yard or a fuel pump being transported as part of the freight inventory?
How much did it weigh?
Was anyone injured?
Could it have been catastrophic?
Without thorough investigation then you could be looking at a repeat with more significant consequences and be left in the position of not having taken all practicable steps.
Get into it pre(another)incident.

Not really sure if "Is this notifiable" is the right question.
Is it significant? Yes
Are there learnings we could take from the event? Yes
...
Get into it pre(another)incident. — Phil Wilkes

I get where you are going with your point, that we should be more focused on what we can learn from the event to reduce the chance of future similar events, rather than the classification of the event itself.
But the reality is notifying or not for a lot of companies has a huge impact on future work because a lot of tenders/contracts are still awarded with H&S assessed as how many; LTI, Notifiables, etc. with no regards to the context or the outcomes/learnings from those events. Or even some companies internal procedures that punish/reward based on incidents seriousness (and so reports get downplayed as far as possible).
Our fixation on judging based on what is easy to measure is what we needs to addressed if we want to get past significant effort being put into classification vs investigation.