I can't entirely blame Quigley for how he's acting. He's an ass, sure, but Duane's existence does fly in the face of everything Kassalynians know about how their world works. If we met a person appearing to be a walking corpse here in the real world, we wouldn't be so eager to accept it at face value, either - except we'd be hard-pressed to explain it differently, while Quigley can just assume Duane is a construct.