I think this is a good question and worth discussing. However, in the example question, I think the OP did not know that the two questions were unrelated, and thought that the phrases had something to do with each other (in which case it makes sense to ask about them together).
I agree that there should be only one primary question, but argue that it can make sense to have related questions as well. Although one answer can be right and wrong, we can have this problem with just one question anyway.
Finally, how do we determine what one question is, particularly when a user might ask for the correct choice amongst several valid alternatives? Should that person then ask one question for each possible pair of alternatives?