He's dedicated enough to his revenge that it was the catalyst behind him joining the police. But while he does have attachments, I'm not sure how strong those attachments are. Strong enough to punch out a more senior detective for slandering his colleagues, but stronger than his goal of revenge? Probably not.

So I'd say it's likely the second, because there is definitely a level of acting going on. He behaves very differently when he's with Danno than when he's with someone from the police. I've got more than one memory of someone commenting that they feel like he puts on a facade.