Wow, that is one laid back robot, apparently nothing bothers him. Nice contrast to Roko.
Part of the situation is that we're not seeing the immediate aftermath of the incident.
It might also be possible that some of the emotional triggers can be switched off in a robot body, especially since a lot of the chassis like his are seemingly more designed for more industrial work even if Punchbot isn't in one.
Hell, that would actually be a very good "safety" feature for bots that can feel pain or some of the extreme emotional responses. For example, being able to not panic and make an injury worse if you can keep your head. Things like a nailgun misfire into someones foot and into the floor, yanking that foot around is going to both make things worse for you, but also cause a lot more pain and make it harder to get out.
Having a safeguard installed to deal with that might make sense.
With things like the butt falling off, well, that's more malfunction than damage in the way it happens, even if you still need repair after it. Same as both being sick and injured tend to lead to the doctors...