My thought is that it was some sort of power loss. It looked like it fell straight down with little to no lateral speed. A possibilty is that he launched with cold batteries, or one of the batteries straight up failed altogether. I don't buy his interference explanation one bit, there was nothing controlled about this. Whatever the reason, he was not flying in a manner consistent with safe flying practices. A few years ago someone posted on here a CS8 that abruptly lost power doing a shoot filming ice climbers, if I recall. His bird fell in the same manner. I think determined the batteries being exposed to the cold was causal.