My vote is for sand/gravel/etc. that made him lose the front end.
Overall it looked like a good crew of riders, riding just fast enough to be fun, mebbe 6/10ths.
Most of them were taking the same lines- on a road like that (out west? Sandy landscape?), I'd try to set my lines where car tires had hopefully dispersed the road funk.
Lucky dude fo sho. Lord knows I've ran a LOT faster than that, back in tha day...
At first I thought he was trying to be cute and reach down to touch the ground but crashed. But it did look like he started to slide a bit right before he reached down.
Around the 24 sec mark it looked like maybe he squeezed the front brake a bit too much and the front started to tuck then panic and survival started to set in. I'm thinking there was a decreasing radius involved there
Not sure if this is the cause or effect, but at the :04 and :24 mark you can hear scraping as well as a dust trail from his right footpeg touching down well before he ever looks to be out of control. Perhaps his peg didn't fold up like it should have?