Perhaps it is also that LLMs are horrible at making any kind of argument and probably wrote a shit paper

They tend to be excellent at churning out pages of high school tier writing prompt slop. The precise grammar, the easy-to-read formatting, and the automatic citations make them the ideal tool for generating this kind of beginners writing.

The problem with LLMs in a writing class is the same as calculators in a math class. Its trivial to learn how to use, but doesn't instill the background into how and why it produces these outputs. It's a literal black box.

The purpose of churning out term papers isn't to provide useful information to your grade-school teacher. It is to practice the art of research, analysis, condensation, and presentation. You're supposed to create shit writing at the early stage of your development. That's part of the learning process. Write bad. Get instruction on how to improve. Write better. Get more instruction. Write good.

Bringing an LLM to a writing class is like bringing a hydraulic press to the gym.

Someone else in the comments said that it's possible (may vary by state / locale) that 65 may be the lowest grade they're allowed to give now. So if that's the case, I suspect the teacher would have given them a 0 if they could.