Kinda reminds you of the old Cannonball Run movie!!
Saw a black sheep cousin win a long wheelie competition at a fair on a TT500 about 25 years ago with his knee in the seat like that. He ran out of track before he ran out of wheelie!
I tried it when I was younger (ie healed faster) & it was the only way I could balance for any distance. Never really felt it was going to flip either.
I don't think he intentionally locks the front wheel, it's just there is nothing to keep it spinning.