[OJFord]

That's my reading too, it's not really 'YX' problem (that doesn't even really make sense to me by analogy?) - it's when someone claims you have an XY problem and No actually you do need X, you just didn't bother to go into why because it's not relevant/none of their business/etc.

I think this frequently comes up in the form Well actually the idiomatic way to do this is not X but X'; but X really was needed by OP due to some unstated constraint. (Because why would you state it, especially if you're unaware that you're doing it a remarkably unidiomatic way. You're just asking how to do what you're doing.)