That gun store owner sounds more like an anti-gun liberal than a human being (note the distinction).
That said, Blucore Shooting range and gunshop here in Littleton, CO doesn't allow open carry in their store either. I noted to them that it is a very unfriendly policy towards their clients, and it does discourage me from taking my business there. The counter salesman understood, and his boss called him back into the office there right before I left. Like to have heard from the boss frankly, because I don't see how you can justify that kind of disrespect and hope to maintain the business. (the reasoning the clerk gave was that they are armed and if someone started shooting they wouldn't accidently shoot an armed person who was trying to protect themselves - borrowing liberal logic).