It means, he is not listed on the register of those interred. There remains many, many unknowns. However,
it stands to reason, he is most likely buried there.

As at Vicksburg, the actual burial locations most likely remain unknown as the originial cyprus, wooden markers have long
ago deterioted.

Register of the Confederate dead, interred in Hollywood Cemetery, Richmond, Va
https://archive.org/details/registerofconfed00holl