It looks like a combination of things, it appears the road surface may have changed, maybe gravel or a tar snake right in his line, his body position wasnt great and he may have chopped the throttle, which would cause the suspension to settle even lower, causing hard parts to hit, robbing traction, slides rear tire even more, which resulted in a near high side. Once all that happened I'm sure he totally tensed up, freaked out, and became part of the landscape. I sure hope he's recovering.
His riding companion? The bike first? Really???