Just look at the rear brake!
He was clearly riding downhill backwards at incredible speed when he hit the brakes. That happens a lot when riders get tired struggling to ride up long hills, (usually on fixed gears with rear only brakes) they loose their strength and start slipping backwards. Their feet are locked into their pedals so they cant put their foot down. Before they know it they are going 40mph backwards and panic, hitting the brakes. The result is that tell-tale seat stay damage called "retro-bend". Very common.