Am I supposed to feel badly about it?

If the boss fired him (and I don't know either way), then address your comment to the boss, not to me. Besides, if he did get fired, what does that say about whether he really was "doing his job"? I was there, he was rude, and I reported truthfully what I experienced. I pointed out that this guard's actions potentially could cost the organization, because his behavior could easily alienate potential residents.