Even though he is young there is really no way to know if he was treated poorly and maybe this is something that is a direct action from her previous home. Regardless, I would get a trainer involved to help you out so that you can nip it in the bud, and I don't blame you for being a bit afraid... teeth hurt.
As far as that video, what the heck is wrong with that guy to think its something impressive that his dog acts like that. I hope he gets HIS arm bit the jerk
