From what we have been able to figure out from a number of sources, the video isn’t from the final retail build of the game. The final retail build has never been accessed or compromised, according to what we have been able to learn.
While the video has been pulled from YouTube early Saturday morning, it is apparently popping up on other video sites. Many are speculating that the video footage was likely taken from the Xbox Live PartnerNet, but that, too, remains unconfirmed at this point.