it doesn't matter if it's his gun or not. what matters is whether he was carrying it, and that it was unregistered. read the statutes he was charged with to figure out what matters.
"A weapon is carried if it moves with you, or if you have it in your possession. Having a knife hidden in your pocket, for example, constitutes carrying a weapon because whenever you move, the weapon moves with you. But movement isn't required: Under the law, if you were asleep with a knife in your pocket, you'd still be carrying it. Even when the weapon isn't physically in your possession (held, pocketed, or worn), it's considered "carried" if it's within easy reach or control. So, a weapon hidden under a car seat is considered carried if it's available for immediate use by someone in the car."
Learn about concealed weapon carry laws—who can carry a concealed weapon, where, and how? And the penalties for violating these laws.
www.criminaldefenselawyer.com