I only watched the crash a few times, and not the rest of the video. Ugh it makes me sad - been there too many times. Crashing just sucks and that video needs a trigger warning ha ha.
The only thing I can really tell for sure about this video is that it was a front end tuck, and it didn't start with rolling off the throttle. So probably not braking either.
One thing I will add, not that I know for sure it contributed: in situations like that where the rider doesn't feel safe - wet road, maybe compromised line, trying to slow for a corner while leaned over, etc. - it's pretty common to tense up on the bars, such that one inhibits the natural correction that the bike will perform over any kind of irregularity. So, like, you hit a low traction bit and the front starts to tuck a little, with a relaxed grip you probably get a wiggle in the bars then carry on. Tight, nervous girip on the bars, the steering can't do it's little natural correction, and down you go.
Same deal on a dry race track at big lean angles - fight the steering and the bike does all kinds of strange stuff, up to and including a low side crash even though there was lots of traction.