Doubtful he went through the trouble of copywriting the test.
The students who posted the questions probably thought they were helping other students and didn’t realize the ramifications of putting the questions on the web would lower their grades due to the prof. grading on the curve.
No one has to do anything to get a copyright.
Every author has a copyright in any original material that author creates, without the need to formally register a copyright. https://www.uspto.gov/ip-policy/copyright-policy/copyright-basics
“Doubtful he went through the trouble of copywriting the test.”
Copyright is automatic. No filing required.
College student cheating! I am shocked! /s
He owned the copyright the moment he made the document. He didn't need to register it.