To my eye this looks like it was done on purpose.
The person doing this is too experienced to have done this by mistake. (or just got really lucky)

Watch the part of the video where he steps off the bike as it flips.
That's not something you would normally do without some experience.

This person likely was testing the limits of the Spyder and was trying to flip it. That takes a LOT of skill to do without hurting yourself.
The throttle control is good until he lets off at the wrong point in the slide. If it was kept pinned the back would have continued to slide easily.

My small bet would be on that Kevin is pretty experienced with hooligan-esc riding and was ready for this 100%.
Certainly would not go as far as calling him stupid. Maybe not the decision I agree with but not stupid.