They don't need, and likely didn't have probable cause to stop this person. It is REASONABLE to believe that the person was carrying a firearm on Simon Mall property based on what the officer was seeing. This allows them to stop them, advise them they are trespassing, and simply escort them off the property while acting as an agent for the property. Had this individual simply stopped and agreed to leave the property the police never would have found that switch. I'd even argue that they have no obligation to let the officers see the firearm, just agree with them and leave. This may require identification to be placed on a trespass list, but I have no idea what exactly Simon Malls requires of the officers working there.So LEO can't use simple gun possession for probable cause while patrolling the street, but can use it when working security at a private venue? That does seem counterintuitive. Again, I haven't read enough of this particular story to know what exactly was visible to the officer. I wouldn't think a 'bulge' would be enough reason, for in-house security or LEO, to stop and investigate the individual. I understand why the mall property owners are sensitive to security issues though. They've taken a beating in the press re: guns and violence at mall properties, here of late.
He only went to jail for the switch because he ran after being told to stop, at which point the Police side of things takes over the agent of the property side. That's the entire point in hiring people with police powers over just security guards.