The paper is not about nerds vs. jocks. It's about athletes vs. non-athletes. There are many athletes that are nerds, and many non-athletes that are not nerds.

However, I do give NBER full credit for scoring high on the clickbait metric. If you download the actual paper, the word "nerd" only appears in the title of the pdf.

(curiously, and as evidence that nerds don't really go to Harvard, they list Aerospace Engineering as an offered major, but with a participation rate of 0.00% across male/female, athlete/non.)