I don’t know how you would find this out - you might ask the school - but it could be 85% of students who have taken most or all of the freshman STEM classes in their AP version and/or scored above a 750 on their math SAT, and a lower percentage of students with less impressive credentials.
I am wondering if schools track these sorts of things. A while back I talked with a WWP parent (to reference another thread) who mentioned that her S barely needed to show up in class to ace his calc 3 and diff eq classes since he had already learned the material in high school. Large state flagship with impressive engineering rankings.