Up in Montana we call smaller calibers pea shooters. My dad has even called a 9mm a pea shooter. I had to correct him and tell him it's a bit bigger than a pea shooter. He relented that it was a "bit" bigger but not much. The way this is decided is by the price of ammo. If you can shoot it a lot then it's a pea shooter.
If I was in that situation I would have been telling them it's a little bigger than a bb gun, but it's still cheap for what I use it for.