I had all sorts of ideas of what to name this thread. But ultimately, it defies description.
All sorts of speculation in the comments.
What I can see is that he wasn't passing traffic at a massive speed differential, only slightly faster than the other traffic that was visible, and the bike starts a tankslapper. What caused it? A botched wheelie?, I didn't see him set a wheelie down. Road debris?, A flat tire?, a bike that is just prone to tankslapping?
I know that a Kawi ZX-12 I had was prone to tankslapping at the slightest provocation.
Anyway, the rider is incredibly lucky to be alive..