The cops made a mistake, fair enough, it happens and fortunately no one got hurt, but for F*&K SAKE, be an adult and own up to it. Repeat after me..."I am sorry, sir. I thought you had a fire arm. I am sorry I delayed you, but we can't be too careful. Have a nice day." Now, how hard was that...
You can guarantee the cop will have the piss taken forever about this... I can't even see how he'd think it was a gun - the big red handles at either end are a pretty big giveaway, but maybe it was just poking out from under the seat - like every other steering lock in the world!