Perhaps I am completely misinterpreting what I saw, but what I think I saw was a second row passenger on the left side of one of the helicopters seeing the other helicopter getting closer from the left and below, and repeatedly tapping the pilot on the shoulder to bring the pilot’s attention to something the pilot wasn’t looking at. What I think I saw was a passenger trying to bring the pilot’s attention to an actual threat of which the pilot wasn’t aware. I anticipate that the ATSB’s report will recalibrate my interpretation if I’m wrong.
(Purely coincidentally, my pre-take-off brief to (usually non-pilot) pax is to ask them to be quiet during take-off but, if there’s something of which they think I need urgently to be aware, to tap me on my shoulder and point at what they think I need to be aware.)
Back to the main subject of this thread, it would be a ghastly irony of the one or both of the helicopters involved in the tragedy had ADS-B IN equipment with traffic alert capability, but switched off due to ‘nuisance’ alarms. I anticipate that the ATSB’s report will be clear about what avionics was fitted and how it was being used.