I don't see how this fits into any armed citizenry narrative. Even jurisdictions that tightly control gun permits allow off-duty police officers to work as security guards.
But you are thinking solely in ted,ms of the fact tat it was an off-duty police officer. (My own father made the front page of late and lamented Philadelphia Evening Bulletin when, off duty, he came upon someone attempting to rob a bank. He pulled his service revolver and arrested the fellow. But he would be the first to say that any armed citizen could have done the same thing. In this case, it is the being armed that counts, not one's profession.