A best answer is considered a violation?

Unfortunately, being chosen as 'Best Answer' does not give an answer immunity. If a question does not make sense, either report it or pass it by. Answers, according to the CGs, must attempt to answer the question. That answer did not, so it was reported and removed as 'not an answer'. Your other option is to see if the asker allows email and email them for clarification. Or, make assumptions, TRY to answer the question, and then ask for clarification.

Actually, asking a question instead of giving an answer is a violation. If you don't know the question or the question isn't clear, then what you really need to do is pass it by. The only way you could possibly answer a question like that and still ask what the question is, is to attempt to decipher what the question might be and answer that way. Then you can say something like "If this isn't what you meant, you need to provide more information." But JUST asking "What is your question?" as your answer... is a violation. The "Not a Question or Answer" response is made to be used both for questions or for answers. So in your case, the "Not an Answer" part is what applies.

It is a question, albeit poorly worded. If you had asked for a clarification on what he meant, that would be fine. Instead, you criticized him for not asking a question, when he clearly did.

For example, a more appropriate answer would be:

"Did you mean 'the most famous country', or 'the least famous country?' The most famous is almost certainly the United States. Many countries are comparatively unknown, such as Mauritania. Did you know that the Vatican is actually it's own country?"