Is there no room for "fun" and "fascinating" questions about culture on a site dedicated to travel?
In all likelihood, the ridiculously popular question became so, due to the notorious Hot Network Questions, and the resulting snowball effect. That would be my best guess, I wasn't a member of Travel.SE when the question was first posted.
Questions that enter the Hot List stand a greater chance of attracting a high number of views in a very brief amount of time. Those views will translate into upvotes if the question is "fun" and "fascinating", or if the answer(s) are particularly excellent. A subpar/mediocre question can appear to be great if it receives an exceptionally high-quality answer. And I think this is what happened here.
Does that mean How do you know if Americans genuinely/literally mean what they say?
is off-topic? Looking at its edit history, we can see that it was never put on hold, closed or reopened. It is, presumably, safe to say that the majority of users (in this community) sustained that the question was on-topic.
However, the success of one question about a specific culture offers no guarantees that a question asking about the favourite dishes of Henan province or which dogs are preferred for the hunting of the silverback tanuki will receive equal enthusiasm.
In my humble opinion, the silverback hunting question is of limited interest and of practical use to a very restricted number of users and visitors. I wouldn't be surprised if that type of question was closed, or if it languished in the unanswered queue for weeks or months on end.
The third question proposed by the OP
I have been in Madagascar for three days and it seems to me Madagascarians love to say X and mean Y. Please lay bare the secrets of the Madagascarian psyche for me to behold!
I would say is off-topic because it is primarily asking about language. The last request “Please lay bare the secrets of the Madagascarian psyche” is obviously sarcastic in tone, I'm not sure if users would appreciate its humour. I would suggest that the OP avoids any semblance of sarcasm in questions, they tend to backfire.
The first question, however, would be on-topic if a bit more context was added.
What are the favourite dishes of Henan province?
It is the only question which specifically asks about a country's culture.