I think their point was just that those numbers (68 for Notre Dame and 16 for Northwestern) seemed dubious.
I looked up the RSCI lists beginning with the 2002 High School graduating class (Dee, Deron, and Augie's class) and ending with 2022. This includes only incoming Freshmen to each school and doesn't account for incoming transfers:
Notre Dame has had 17 freshmen ranked in the Top 100 in their respective classes, and Northwestern has had 4, so your point still stands that it's a lot easier to recruit Top 100 talent at ND than NW.
Just for fun, in that same time frame, Illinois has had 35 incoming freshmen that were ranked in the RSCI top 100.