I think that's the point, the bike example shows people have some concept of what a bike is (pedals, wheels, frame) even without an exact understanding of it, or a precise image in mind.
It's the same for "draw a house". You may do a square facade, triangular roof, windows, chimney, door. It is equally unrealistic, because people don't have a clue how tall floors should be, have no sense of proportion etc..
It's just that in the bike case it's more obviously wrong.
