[clock86]

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.

[jabagawee]

Would a diff/patch be DMCA-proof then? Or would it fall under derivative works?

[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.

[lmm]

APIs shouldn't be copyrightable as they're necessary for interfacing. The solution to a homework problem shouldn't be a derivative work of the problem, and so it should be possible to distribute the solution in a way that doesn't infringe on the university's copyright.