As someone who teaches astronomy, I can say I'm not surprised, and it's not about religion or politics. Moderate has part of the answer - people generally don't retain facts that don't apply to their everyday lives. Xahar also has part of the answer, when people hear an unexpected or unfamiliar question they easily misunderstand the question. One of the best predictors for success in college physics or astronomy at the introductory level is not one's math skill, but rather one's reading skill.
But astronomy doesn't apply to my everyday life and I still retain that information. I don't understand why it's so difficult to retain such a basic fact. I'm a history guy, I don't do math or science. By that logic I shouldn't be able to remember that the earth revolves around the sun.