There is earlier reference to a Navigator in the first few pages of this thread. It discusses the fact that the same Navigator was on both demo flights.
Even though the plane is 2-crew there may have been additional people on the flight deck.
There already was a third person in the cocpit - a potential customer. Reportedly he dont disturb the pilots, only from time to time he asked some question, about consumption of fuel etc. No wishes for risky maneuver or sightseeing. Hypothetical navigator shoul be a forth person in little cocpit.
adding:
There was the navigator aboard - Oleg Shvecov