Well its easy to be critical but just maybe his tyres just weren't grippy.
That would account for the tentativeness and the skid.
I'd have thought poor grip would have washed out the front wheel? It's not like the bike is leant over very far though.
I'm with the others here, there are moments of fishtailing on several corners before he loses it which suggests a lack of cornering confidence and rear braking during the corners. Eventually that catches up with him.
Hopefully bike and rider are OK and lessons have been learned.
He's popped the rear tire.. And not had the instinct to get his weight forward.. You can keep a bike upright while very sideways once your over the bars.. Riding sweet fixas on the road with no brakes makes you a gun at doing just that
I'd say he's killed the clincher tire via over heating the wheel by dragging the brakes too much.
Unlucky, but the only thing I have to say about it all is.. If your gona coach some one into descending fast you DON'T do it from behind..l
that's pretty stupid... Auctally very stupid.
Best way to learn good postion and lines is to follow or be lead down a hill by some one fast and confident.. Doesn't look so good on the go pro but he wouldn't have cocked it up so bad.
Also carbon clinchers, learning to descend with vigor is pretty much s recipe for, well finding your self sliding along on your ass.. If you can afford lightweights you can afford to ride tubulars..
Lucky he's ok