The article is dated in March and has phrases like "Admitted students have until May 1 to accept the University’s offer of admission. Brown anticipates an incoming class of approximately…", so it sounds like an estimation before many admitted students made their decision about whether to attend Brown or elsewhere. I believe the official university numbers are on the ones I listed, as published at http://www.browndailyherald.com/2018/10/12/university-yield-rate-hits-time-high-61-percent/ .