Another valid response if you think it is an XY problem is to ask for more information. Or even do all three: "Here's how you do X. But if you really need Y, then you should do Z instead. What are you actually trying to do here?"
Also, if somebody can answer Y, but not X, are they really qualified enough to answer the question?
Maybe. It could be that there just isn't an answer to X. Or the answer is "you can't", so the author tries to give an answer that is more helpful, in case the asker actually wants Y (it would probably be good to explicitly explain that though). Or maybe there are multiple ways of interpreting X, and the answer interpreted it a different way than you expected.
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Another valid response if you think it is an XY problem is to ask for more information. Or even do all three: "Here's how you do X. But if you really need Y, then you should do Z instead. What are you actually trying to do here?"
Maybe. It could be that there just isn't an answer to X. Or the answer is "you can't", so the author tries to give an answer that is more helpful, in case the asker actually wants Y (it would probably be good to explicitly explain that though). Or maybe there are multiple ways of interpreting X, and the answer interpreted it a different way than you expected.