No your theory does not explain how the OP’s coin has no obverse rim. If it is perfectly smooth on one side only then it was most likely milled, sanded, or smoothed down.
Just to play devil's advocate here.... Would the pressure of the strike be sufficient to flatten an upset rim, particularly if two planchets faced each other?
Ok........hope nobody died holding their breath!! Finally figured out how to take a decent close up pic and BAM..everybody's gone!? WTH!!? Must be supper time!? LOL!
that surface was ground down and polished many years ago. The theory of two planchets in the press at once doesn't work because the excess pressure created would have at least warped the surface.
I suppose anything is possible, but most of the capped dies and uniface strikes I’ve seen online still have at least some rim. I am not an error collector but as do like to read about them.