@sphennings Well obviously stack exchange has rules about what questions can be asked. Certain questions don't fit. So it wouldn't be at all strange for it to simply be impossible to ask X, and so substituting Y wouldn't happen by mere mistake, but by necessity.
This seems like it would mostly happen when X is too broad. You want to ask X, but you can't, so you think of a specific way to solve the X problem, if only you knew the answer to Y, which is naturally a more specific question. It's a recipe for the XY problem.