I would have handled the situation differently. The law doesn't say you have to prove to anyone but a LEO that you are legally carrying a gun. The manager had no legal right to ask and see your CCL. If he would have came up to me and asked if I was a cop I would have told him it's none of his business and I would like to be left alone. It is his right to call the cops and have them come and check my CCL. I will show them and then I would let them explain the law to him.
If someones first question is "are you a cop" then you can guess they have a fear of guns and have an opinion that only cops should have a gun and are ignorant of the law. Any discussion after that would be a waste of time. Let the cops explain the law because the manager won't believe or care about anything you say.
Try this approach and see how quickly you get arrested or cited for trespassing. The douche approach will end up causing you more harm than good.