I heard this one before....
Well the Prometheus Crew have Blue Suits but i do think if the person is telling the truth that they would be able to tell whats Alien looking and Human in Space suits.
Maybe the guys are Jockeys? Remember their are 4 Jockey sarcophagus on the Derelict?
I dont think Ridley would go for having at least 4 Alien Xeno looking Creatures running around in the movie? But then something powerfull has seemingly killed a fair share of 9ft Space Jockeys.