I'm not convinced that it's "stupid" to read SF stupidly. I think putting the same story in an unfamiliar context increases the amount of work it takes to understand it, and so decreases the expected net reward from reading it. It's rational to put less effort into tasks with lower expected reward, and in this case the study participants are right because the alien setting has no material effect on the story; it's gratuitous unfamiliarity with no telos.