If I saw somebody pull out a rifle from their bag and pull it to their shoulder like they are going to fire - that's an entirely different story. If they pull it out and hold it by the pistol grip and walk around with it - that, also, is an entirely different story.
I would hope some brave citizen would take action....since if anyone from law enforcement asked him about it would be an infringment on his rights....better yet, maybe somebody did! Bet some of the keyboard commandos are waking up to email off some angry letters to the airport