If you have adjusted the seat height yourself you know that the seat tube slides within the frame. So the first/left-most bicycle is wrong because the seat tube is vertical and the frame tubes are at angles. Then you scan the four diagrams to find the one where the seat tube and one of the frame tubes form a straight line. None of them.

At this point you give up and just answer randomly.

The experimenter claims "People made lots of fundamental mistakes." but I think the experimenter made a fundamental mistake and his subjects lost interest in the experiment.