[zedshaw]

tl;dr If you fork and don't pull-request then that's the violation.

That's the point. If you fork and don't do a pull request so I can pull it back, then you're leaving an altered copy out there. Can't do that. If however you do a pull request and I pull your changes in, then your fork is no longer an alteration.

This prevents people from butchering your work because they think they know better and then leaving half-assed junk out there to screw students over, but still lets people contribute fixes.