This sounds a bit like you dislike the lack of understanding, which itself is based on lack of understanding.

On the other hand I agree that commenting on ones disability is a break of boundaries in most contexts. One should quite often avoid to comment on traits in general that are irrelevant for the context or the conversation.

It is not about understanding, it is about not even trying to and just telling a complete stranger how you think they have it bad. That is, as you identified, a break of boundaries. And, frankly, if someone breaks into your house, you are not obligated to "understand" them. You just know they are shitty humans.