His decision to become a basketball player will not alter that fact. The question is whether the paradox succeeds in making the opposing arguments equally strong. I don't think the two arguments are in fact equally strong, for, given the setup of the paradox, one can find a reasonable explanation for the alien being's ability to predict correctly. And in that case, the argument for taking the closed box is stronger than that for taking both boxes. In order to explain why taking only the closed box is the more reasonable decision, let's first consider what it means to predict something.
Prediction can mean at least one of two things.
Nostradamus isn't supposed to have been just a really good weatherman, he is supposed to have foreseen the future. This second kind of prediction is the equivalent of information traveling back in time. Now, whether the prediction is scientific or prescient, the solution to the paradox is essentially the same. But since I don't accept prescience, and because I don't think that that is how the paradox is usually understood, I will limit my explanation to scientific prediction only. If the being predicts in the manner of a scientist, that means that there is a certain state of affairs, A, which holds at some point in time prior to your decision and the prediction, and which causes both.