The whole purpose of the DMCA safe harbor is that if the DMCA process is complied with, there is no liability of the host to the content owner; the user submitting the content may still be liable, but that requires the copyright owner to take legal action against that user.

In order to qualify for DMCA safe harbor, the site has to 'have no direct financial benefit' from the content (https://en.wikipedia.org/wiki/Online_Copyright_Infringement_...)

In the Napster case, the fact that the infringing content drew in more users was enough to prove it was financially benefiting from the content. Even if Udemy refunds all the class fees for the infringing classes, they would still get the benefit of bringing in new users to their platform because of the infringing content.

In other words, it might be hard for them to claim safe harbor.

I'm surprised at the choice of words. "potentially" doesn't quite cut it.