This is nonsense. An encryption key can never be copyrighted, it's only illegal to redistribute it because it's a circumvention device under the DMCA, and possibly illegal under the CFAA, not because it's copyrighted.
I wish people would point that out more often when there's discussion around backdooring systems to allow for government surveillance. With how quickly keys got out for HDDVD and Blu-ray, there's no reason to thing something similar wouldn't happen with a government backdoor, and that's if it's not for sale on the dark web before it goes public.
Actually refutes your claim that an AES key can itself be covered by copyright.
The given reason to attempt to have it removed was not that copying the key itself violates copyright, but that it was used to circumvent copyright-protection mechanisms.