I'm only vaguely knowledgeable about antique guns, and it seems the definitions aren't generally very definite. Size wise, this is smaller than some punt guns. So I went back and read the yahoo article, and the article said it was a wall or rampart gun. I would guess the big difference between a wall gun and a cannon, is, the wall gun was small enough to be picked up and moved by one person.

who you've been ain't who you've got to be