clock86

I'm guessing it is more likely that these repositories were searched for by staff/professors than fully specific code was searched for.

I don't think you can claim that changing code absolves you of copyright issues, it might make it harder to find though.

I think it should have been easily provable that you owned the website and that your code matched, any sort of escalation beyond initial talking with professor should have resolved that. If not that is absolutely ridiculous.

No, often when assignments are given out you'll also give students large chunks of code or libraries to modify or work with.

The DMCA says that is what the infringement is.