I think there was misunderstanding on both sides. From what I've learned, the manager was NOT happy about the guy with the AR15. But I don't think anyone went and asked the OCers to leave either.
Regardless, I don't think OCing a rifle in an urban environment is a good idea. To my way of thinking, I carry a pistol for defensive purposes. A rifle is more of an offensive weapon. It generally takes longer to get into action, from an apparent slung and "safe" position, compared to a pistol. It's also unnecessarily excessive bulk, compared to a pistol. Heck, I wouldn't even pack a pistol version. Period. Too much chance of it being mistaken for a short rifle, or SMG. And until we get the general populace used to the idea of handguns, why alienate them further with stuff like that?
But, that's just my opinion.