It's not lunging at the guys face. It's backing away after the guy grabbed at his leash at that point in the video. If it was lunging it would have bit him. He just kind of nipped at the guys arm and turned away. You could tell the dog knew better than to bite someone. It was confused and didn't know what to do.
An aggressive pit or rottie comes on like a brick shithouse and basically there's no stopping it when it's that close. If that dog was aggressive the officer would have been bitten, he wasn't.