That is coming off a long fast straight 200+mph. They think as he came over the crest he pulled the brake to scrub off speed. Cause the bike was unweighted coming over the crest it grabbed when the bike settled.
Of course he doesn't remember. Amazingly we was walking around on Sunday.
Worse thing about the video is the sound when he hits the ground. Not in the video above but in the original one when watching the race.