At one table I'm looking and the guy has a few AR's, he then ask me "what are you running now"?
He probably just made the assumption that you were a competitive shooter or participated in regular training & practice. For someone like that, the firearm is a tool that helps them perfect a skill and accomplish a goal -- not just an object to be possessed.
It's the same thing as asking someone, "what car are you driving these days?" They may own a pickup, motorcycle, sedan, a street rod, and two economy cars. But you're asking what they're concentrating their time in/on. What have they found to accomplish their goals efficiently and reliably.
At a gun show, I would not ask a tweedy-looking fellow squinting at a new-in-box S&W Registered Magnum through a jeweler's loupe, "Hey, what revolver are you running now?" The question doesn't apply to his (perceived) interests and habits.
But someone at the next table comparing Aimpoints and ACOGS on an AR-15 with half the finish worn off probably "runs" his system pretty hard.
Or the guy in the USPSA or IDPA match t-shirt who's buying another two cases of ammo, like he does every month.
The question might even apply to the Alaskan or Rocky Mountain hunting guide trying to decide between a light .375 and a heavier .458 as his back-up gun for Grizzly hunts. Guys/gals for whom ownership of the weapon is not the destination, but a means to an end.
I don't know why he assumed you fit into that role. Maybe he was just trying to flatter you.