The other (later??) Style has wrench flats on the ball stem that screws into the hanger. So presumably the ball is fitted to the back with screws and the protruding stem is screwed into the hanger.
Your type does look an assembly puzzle. Maybe the plastic was hot moulded around the metal ball after it was put through the hole in the back or the ball was some how attached to the hanger, screw and glue???
The screw spacing in the back looks to be the same on both types but the big hole for the stem seems to have different size for each type.