It's a little like when I was explaining to a small group of family about a new (to me, anyway) way to fill a cup of beer. There was a cap at the bottom of the cup, and the bartender held the cup over a post, pushing up the cap and filling the cup from the bottom. My aunt looked at me, confused, and asked, "But don't all cups fill from the bottom?" I guess they actually do, right?
I'm not one of those who argue that language is vague and confusing. I think the poor use of language and/or honest error either on the part of the speaker or the listener can make it appear confused. Still, the little incongruities can be fun to notice.
Sort of like, when we were loading trucks back in the days working with my grandfather, Grandpa Joe would bark, "Raise 'er down!" when ready to place a load on the truck bed.