> in the case of riddles, it doesn't matter that there are no trains in the Arctic in reality
That's quite the claim. Riddles aren't constrained to reality? Well then the polar bear one can be answerd with purple too.
And as you point out, the average person would also be confused - "I don't know, purple?" would be a reasonable response. Because the question is dumb in the first place
Knowing about train tracks is not that different from knowing about magnetic poles or the common habitats of various bears. All these pieces of data are fairly basic to an educated person. Both the polar bear riddle and my variation of it depend on this body of knowledge.
If you don't incorporate outside context at all, then things start to get confusing quite quickly. What even is a bear? That information wasn't provided! What color is it? Well, what even is color. None were defined. See, it gets ridiculous fast. You clearly need to depend on knowledge that is not presented. Knowing about different colors or different bear habitats is common. Neither needs to be defined in the question.
In the end, both of these bear riddles test whether the answerer considered more than one degree of separation. The ability to consider second order effects and beyond [1] is a sign of an intelligent person. Not every human passes.
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