What exactly does being cautious mean here? Should people get some bulletproof vests? Should they hide behind columns and corners?
His stunt shouldn't cause a panic. Should people become cautious of him? Sure. Should the store ask him to leave? If they want to. But there's no reason to start panicking.
If this guy wants to start shooting, people around him aren't going to have time to do something to avoid the bullets. Unless by being cautious you mean they need to carry their own firearms, watch the guy closely and shoot him if there is an indication that he's preparing to shoot.
If something goes wrong here, it's not like the store is going to magically protect those people, so whether it's an act allowed by the store or not, it really doesn't make a difference to people who fear for their lives.