Agreed.Fellas, I think he's actually going very slow when he finally dumps. With the rubber already burned in the pavement to the left, looks like he locked up the rear and it swung around, he was almost stopped and the momentum made him tilt and lean over... almost as if you just lost balance and fell over... the whole sequence of the fall he hardly moves laterally at all, and his leg is almost fully extended downward during his tumble rather than his upper torso leading completely and legs trailing... estimated forward speed 2-3 mph during the fall.
As for the tires, I don't think they have anything to do with it. As Bill mentioned I think he 'entered' hot and locked up out of shock of the turns down and right angle, locked it up, swung the rear around and fell over.
Personally I think it was a really cool sequence, and bet the guy is just fine (wounded pride aside).