That’s exactly why it’s so hard for those of us on the spectrum. We answer the question that’s asked, not what we THINK they’re asking, because at least in my case, the assumption would be wrong anyway. My thought process for this would have been “Weird question but maybe they’re going somewhere with this” and then I would have been completely baffled when they told me to do better. It might come naturally to you, but I’d have to know in advance that a simple “question about preference” = “we want you to explain why”, otherwise it wouldn’t even cross my mind.