Bucky's not planning to shoot anyone if he can avoid it, but he's not against pulling his gun up an holding it like he's ready to. If anything, it will be a deterrent, but in a fight, Bucky would rather use non-lethal force if he can.

The fact that the guy can tell what gun he's got on his back from across the room is impressive. It's the kind of thing Bucky can do, but it's a pretty specific skill.

"You work with guns before?"

He positions himself so that he's got an eye on all the ways in, but he's also got an eye on his new friend. The kind of guy who thinks people will attack him over parts can't be more than a few steps from someone who'd at least think about attacking others over them.