It’s like that with anything - you can never completely define something that is not just a figment of imagination (and maybe not even that can be properly defined). Language is based on luck, at least partially. But when you ascertain ‘not Y’, in the case that it is not understood, it is way more clear. In fact, I’d say it’s much more clear to say what something you mean is not rather than what that something is. In any case, it’s all good to have a go at answering in whichever way possible, then when that has been cleared that (for example) taste was not at stake, to insist there is weird.
Quite the contrary, I’m asking what is true. If I was asking what they think is true, I would ask “Do you think X is true?” instead of “Is X truth?”. If you say I believe some korean band is the best I’d say yes. If you say is that truth? I’d say no.
How come it doesn’t make sense? I don’t think it probably won’t, it just probably won’t.