Yes, he needs to file a nonresident return for DE. And he is probably going to need to file a federal return. Both of those can be done manually, but he can e-file for free, if not through TurboTax, then through the IRS Free File. I suggest the Free File only because of the nonresident DE tax return. With all of the covid delays, I highly recommend e-filing this year.
Do I need to file a federal return this year? There is a link included if he is a dependent on your return to verify whether or not he needs to file. Even if he isn't required to, he may want to to get his withholdings back if possible.