I agree that the author doesn't get to dictate the reading of a poem (nor does the test-maker), but these questions are usually formulated to explicitly reference the intentions of the author (the "author's purpose"). Although, now that I look at a few, it looks like the common language is "The author most likely did so-and-so in order to...".

But more honest language ("What does this line mean?") would erase the veneer of objectivity; hermeneutical questions do not have "right" answers you can pick from a list of multiple choices.