I think that the dog is nothing more than a cheap prop. I can also be totally wrong.
Why would Joey, an 80 year old frail hollow shell of a man want a Bad Ass Looking German Shepard? Maybe Joey thinks the dog makes him look tough. But if the dog was truly a prop, then it would be so well trained that unless someone is choking the shit out of Joey, it would be the most docile animal imaginable.
So, lets say that the dog is a prop, but the training sucked or sucks. How many people on a given day “manage” the dog? The poor dog is confused who his “owner” is and most likely acting out of fear or frustration.
Joey is an asshole and what’s happening to the dog is just plain animal abuse.
You are probably correct...the dog thinks he has to protect too many people