I think this is where the threads usually start to make a turn for the crazy. No one mentioned any crimes being committed nor has the OP ever stated that anyone asked him to leave. He was asked to put the firearm in his vehicle, he refused and choose to leave. No one asked him to leave and no ever stated any crime had been committed.
Thats why I asked where the where was a crime committed that gave the Police the authority to interact BEFORE the manager spoke with the op. THERE WAS NONE. Well not unless you go back into the kitchen. Even though he was asked to put the firearm inside car, it's still telling the OP he needs to leave the building with the firearm.