"School" is an umbrella term for anything that has students and teachers, holds classes, etc. A university is a kind of school. It's easier to write "school" than "university" and in the quote you have it would be confusing to use "university" in place of "school" because it could be read as if Frias broke the record for all universities rather than for his particular one whereas given out usage, we all understand that breaking a "school" record means you've broken the record for whatever educational institution (university/college, high school, middle school, etc.) you attend.