Great photos! Nasty video!
My view would be both riders involved in the crash are to blame and no others.
The slow overtaker did not use his mirrors - I think this is fairly apparent as he did not see the second party approaching with speed, he also did not see the video taker as im sure he had to brake pretty dam hard (hence a bit of wobble on the vid). He also did not check his blind spot otherwise he would have seen the video taker.
The second party was (although on an open speed limit road with other super fast riders) riding too fast for the traffic on the road full stop and was just unlucky there was a numb nut pulling out.
Hopefully both were able to make a fully recover and take something away from such a nasty crash.
