William managed, through excellent self-control, not to bridle with offense at Professor Trohman's tactless and almost certainly inaccurate comment. Instead he changed the subject back to one they'd been discussing, which would hopefully - if all went well - lead to opportunities for further discussion (and school pride) in the future.
"Would you be willing to teach me?" William inquired abruptly, deciding on the instant that it would be worth the risk of getting caught if he succeeded. "We could make it an independent study, if you needed an excuse." That was as close as he was going to get to sharing the fact that he hadn't graduated, and was technically not in possession of a complete education. Professor Trohman could either discern the rest, or William would make up another excuse.