I've seen the NTSB footage of the plane and helicopter crash in Washington. It is practically impossible to discern a landing plane over the lights of a big city at night. Next, the truck had been angled away from the plane approach, so it was coming from the right side (passenger side) and at back. There was zero chance that firetruck could have seen the plane in the seconds it covered hundreds of meters, flying at 200+ km/h. And also in that NTSB investigation there was a case of missed comms, when ATC recording clearly showed controller saying an important word, but it jot "jammed" in the process and there was silence at the receiving end instead of that word (in the middle of the transmission). Not saying it was a case here, but it is possible too.

Just like in that collision, it is possible there is no one single person to blame (apparently helicopter pilot was not outside of the legal corridor, despite the speculations), but it was a compounding error issue.