> The professor just really liked tcc for some reason.

Perhaps, or maybe they just got tired of students coming in and claiming that their program worked perfectly on such-and-such compiler.[1] It looks like tcc would run on most systems from the time of its introduction, and perhaps some that are a great deal older. When I took a few computer science courses, they were much more restrictive. All code had to be compiled with a particular compiler on their computers, and tested on their computers. They said it was to prevent cheating but, given how trivial it would have been to cheat with their setup, I suspect it had more to do with shutting down arguments with students who came in to argue over grades.

[1] I was a TA in the physical sciences for a few years. Some students would try to argue anything for a grade, and would persist if you let them.

Seems like a good way to get students to write C rather than GNU C.