not "Michael Moore's bodyguard but only "a bodyguard who was once assigned to protect Michael Moore"

The reference clarifies the story that one of Moore's bodyguards had been arrested on a gun charge. Evidently, Moore contracts his armed bodyguard service out to others and, while the individual in question, had been assigned to Moore at some point, he was not at the time of the gun arrest.

But while there is some delicious irony in the thought of an employee of an anti-gun zealot being busted on a gun charge, the real issue remains the hypocricy of liberals like Moore who want to be protected with firearms but are happy to deny that right to everyone else.