It’s called competency-based admission.
Read about it here: https://www.aamc.org/download/308462/data/admissionsinitiativesummary.pdf
And USC is far from the only school that has no specific course requirements. Neither does Duke, UMIch, Oakland-Beaumont or several other schools. In fact, all allopathic medical schools are transitioning to competency based admissions to allow students more leeway in fulfilling admission requirements through interdisciplinary science classes, often under non-traditional course names.
The fact USC says there are no specific course requirements, doesn’t mean that you can take whatever classes you wish or take them as P/F classes. If you consult the MSAR, you’ll find that USC has a rather lengthly list of “strongly recommended” coursework (in med school speak, strongly recommended = required) that successful applicants will have, including coursework in genetics, organic chemistry, biochemistry, inorganic chemistry, cellular biology, molecular biology, sociology, physics, ethics and Spanish.
Competency-based admissions for med school has not bearing on that fact that individual colleges are unlikely to allow students to take upper level electives in a discipline without first taking the requisite introductory level classes. (Unless you have advanced standing thru AP/IB credits or pass college-specific placement exams.)