Well, I would let him know by saying something like "Excuse me?... Your rights are showing!" and winked or something like that.
Seems like the guy may have been having a bad day.
If he had been more responsive to you, you could also have engaged him in a discussion about legal OC.
If you have a permit to CC, then you can OC or CC as much or as little as you like. OC can be just the grip of the gun showing, but an LEO might think you're trying to conceal and request your CPL, but as long as it's not ever concealed by a jacket or something like that, then you should be okay, I would think.