Why did gun store sell to him in the first place? Don't they have the right to refuse service to anyone? If you own a gun shop, why on earth would you sell to someone crusading against the right of others to own a gun in the first place? I have seen gun store owners refuse to sell to people before. It's not uncommon.
Last I checked, it isn't illegal for anti-gunners to purchase firearms. Is it the store's right to deny sales to someone? Sure, but I can imagine the backlash from that would have been worse than what they are feeling now. I asked a few questions of some of the workers there, and they aren't allowed to tell me anything. Personally, I'm glad they sold him the gun. It has worked against Mr. Kelly and his crusade.
On a side note, there's a new sign at that particular gun store prohibiting any kind of photographs or videos.