j45 parent
I think it means every time AI is used, it will detect it 80% of the time. Not that 20% of the class will marked as using AI.
you're missing out on the false positives though; catching 80% of cheaters might be acceptable but 20% false positives (not the same thing as 20% of the class) would not be acceptable. AI generated content and plagarism are completely different detection problems.
For sure.
False positives with technology that is non-deterministic is guaranteed.
It's more than slightly comedic people being amazed when LLM math works as it's created to.