If a question does not provide satisfactory basis for a person to give an answer, then yes it should be hidden. Generally that would be enforced for posts that don't really pose a question or have entirely unknown answers -- but if we enforce this on those posts, then I guess it's fair that it also would be on a post like the type you described too. Exception shouldn't be made because one post is "closer" to being answerable than the other, the bottom line is that they're both unanswerable.
However, this would very much be enforced on a case-by-case basis. I'm sure there are posts like this that could be answered well based on assumptions, and others that could be answered if detail was given on every possible situation should there be any ambiguity. So that it's clear what I mean by that: if someone asked a vague question about where they could find a certain berry without specifying their game, I would allow that because you could answer that post with locations from every game that includes that berry.
As for the post you linked though, I don't think that falls into this category, because the answer to it could be found by testing Rotom-Fan and seeing if the same result occurred -- the asker did respond when more detail was asked of them.