I've watched the video upteen times and it appears to show a slow left turn which would have kept the tail wheel on the runway before a large input of right boot whisks it off. Even if the crewman ('f*ckwit') sitting in the left hand doorway had appreciated the situation he wouldn't have had time to stop it with a warning shout once the right turn started. We of course have no idea what was actually going on inside the aircraft, have we?
At the distance the aircraft was from the video camera it is hard to tell just exactly how close to the edge the aircraft actually was and even if the crewman had already warned the handling pilot there's no knowing if he was ignored or even heard over, perhaps, ATC chatter. In short I think it's easy to jump to conclusions but not advisable without knowing all the facts.