What was taught in school over an entire semester usually was a single lecture in university. At least for the mathematics courses, where actually similar things were taught, just from drastically different perspectives.
If you're capable of university level mathematics then you're probably not the audience that school mathematics classes are most concerned about. It's unfortunate, but schools are trying to raise their average grades and your grades were likely to be good regardless.
Surely you had peers at school that found mathematics to be challenging, or even struggled?
