Especially with younger kids, when they are asked a question by someone with authority, there is a reasonable presumption that it can be answered. I'm all for teaching them to challenge that presumption, but I think you'd get a more fair result if the question was, "Can you figure out the age of the shepherd if you know how many dogs and sheep he has in his flock?"
Agreed. I think this is also an issue with the way we teach; we should teach students to have the confidence to deny the solvability or soundness of a problem on their own (rather than forcing irrational thought in order to arrive at a solution). This is the equivalent of teaching a programmer to "shut up and code", even though they may have objections to the proposed solution.
I get that this is supposed to outline the differences between structured / unstructured learning, thinking, and classroom conditioning, but it's not quite fair to draw a conclusion that doesn't take that conditioning into account.