To me it sounds exactly like they're playing the two instruments on top of each other, if not 'side by side' - which is to say, not like something I've never heard before.
Agreed, I was quite disappointed. I actually thought we would here new sounds humans have never heard before. This was more like two instruments picked from an orchestra or, playing two bank settings on a synth on a split keyboard.
The instrument blending is unique, but agree that this was utterly underwhelming.