That is scary to watch.
With the hedge I'm thinking he's only seen the truck a second or so before impact, and looks far to close to centre line as the bike comes into shot, I wonder if had nothing been coming the other way if he would have stayed right side of the road or not.
Possibly a graphic example of target fixation?
It looks to me like the left leg is out and foot off peg while the bike is up, before crossing the centre line, as if an instinctive reaction to bail out has kicked in, rather than to tighten up and get round. There are some natural instincts we want to coach out of ourselves.