Perhaps that's just Aussie terminology, the receiver is the square bit that the hitch (the piece with the tongue attached) fits into. It gets held in place with a horizontal pin and R clip.
Had I read you original post properly I would have seen that you already mentioned that.
I just thought it was interesting that the NZ unit has a substantially lower tow ball weight rating that the US or Aussie one yet still has the same max tow rating.

These OEM tow bars are getting harder to find here too.
New ones were NLA years ago and it took me about 6 months of looking to find a genuine second hand OEM unit. Now to get it sand blasted and powder coated.