That would be my vote, too.
Out in the rathole, I've got a bag with a floor nailer, hammer, and boxes of nails. It's in a spot that I can't quite reach safely, so I can't confirm my memory; but I recollect a shape similar to the picture in your original post. I'd never thought about the uses of the flat metal end, but it does make sense that the rectangular shape could slide along the floor against a block of wood (scrap of flooring) used to knock a new strip of flooring into place before nailing.