Another one was many years ago when the guy asked if the gas operated shotgun he'd just bought took regular or unleaded and asked where the "tank" was, and yes, he was serious...
Not at a gun shop, but my boss (for a very short time) years ago bragged about his .50 cal Desert Eagle. Said it was really accurate, but a hassle to shoot because it took CO2 cylinders. I asked if it was a BB gun, nope, "it shoots 50 AE".
Figured out later he'd heard they're gas operated and thought that meant it ran on CO2; obviously he'd never owned one.
So that makes three of us, accounted for, that have had 'discussions' about gas operated firearms. Amazing. Of course the guy I was talking to quite literally thought I had a gas motor (I guess in the buttstock?) somewhere in my rifle...sounds like your guy just got confused by his paintball gun.
Brings up the timeless debate. If an AR-15 is gas operated would an AR-10 run on diesel? Good stuff.
Another "gas-operated" giggle.
Hunting one day with an acquaintance, he is carrying a Remington 1100 and I have an A-5 Browning. I remarked on how convenient the gas operated system made changing ammo vs my Browning. He had a puzzled look and asked "Gas operated?", and I says yes.
His next remark made me laugh.
"I hope it don't run out on the next covey..." I explained gas operation to him. Don't know if he got it, though.
