The wheelie was intentional. He definitely didn't intend on the wheel going that far back. It was a quick joyful victory(?) wheelie. If you look closely you can see him tap his rear brake as he is about to loop it, which in turn saved it from looping. You can't see it in this video but when the front end slams back on to the track he experiences the tank slapper from hell. Apparently he saved that as well.