No, Trump is not setting a precedent.

The Court is following the law as stated in Executive Order 13489 which is from 2009 and gave the public greater access to Presidential Records after the Bush White House tried to restrict them. As far as I know this executive order hasn't been superceded.

The incumbent president is the decider. There's a whole section on executive privilege claims by former presidents....... Sec. 4. Claim of Executive Privilege by Former President.

In this case, the claim goes to the Archivist.
" the Archivist shall consult with the Attorney General (through the Assistant Attorney General for the Office of Legal Counsel), the Counsel to the President, and such other executive agencies "

Then the Archivist’s determines if it's a legitimate claim but "In making the determination referred to in subsection (a) of this section, the Archivist **shall abide by any instructions given him by the incumbent President or his designee unless otherwise directed by a final court order. **