Yes, criminals do research, these are clearly very intelligent people who staked out the place, knew exactly what place to rob and all that, all for what? $50?
The overwhelming majority of criminals are not all that bright, they don't really care, they drive around high as hell and rob a place, any place.
I doubt that not allowing firearms on their premises had anything to do with them getting robbed BUT if this is the case then every single other restaurant, shop or what have you that do allow it should stand as counter evidence that it doesn't help to allow firearms on your premises.
I think you'll find, if you can get over your gloating, that the occurrence of armed robberies are about the same percentage wise (perhaps a bit lower for places that do not allow firearms but that is only because they are more niched establishments).