This is going to sound odd, but stick with me..that dog isn't acting genuinely aggressive in my not-at-all-expert opinion.
It's playing a fun game (in its own head, in reality yes it's attacking people).
The way it's doing a jump for the arm, after a lollopy waggy tail chase, makes me think the arsehole owner has been doing 'defence training' with it. The 'chase then bite a padded sleeve' type. The dog looks happy and relaxed and confused someone's bashed it. It lets go immediately, which I don't think it would do in an aggressive attack.
This is in no way a defence, more being grateful that it could have been a hell of a lot worse and wasn't. And if I'm right, shows exactly how much of an irresponsible dickhead it's owner is.