I don't agree with that. The pronoun "this" does not appear in the example question you just provided. There's a difference between "this" and "his" and the difference is how they resolve contextually.

And in the OP's question, it's obvious that "this" resolves to the current question that it appears in. It seems like you want to say that this is not obviously the case simply because the question is unanswerable. Yet I'm not convinced that you didn't invent this requirement yourself. Anyone reading the OP's question would clearly understand to what the "this" is referring.