They are copyrightable as works, and even if they arent then they are as devices protecting works.
The level of creativity needed for copyright is minimal. A key pair is generated by machine, but at the request of a human according to parameters selected by the human. That is likely enough.
Since recipes are not protected under copyright law [1] it's unlikely mathematical parameter lists have sufficient "literary expression" for protection.
OTOH, a passphrase of substantial creativity [2] may be protected by copyright. Crucially (for any takedown), this would cover transformations by key derivation functions.
A purely random number is almost certainly always beyond copyright, but as soon as someone puts limitations on that randomness a court may find that enough.
And what matters for a takedown is not the number, but the actually document being published. Github is not hosting the random number. It is hosting that number in the context of a larger document and it is that document that is subject to the takedown request. Things might be different if github hosted only the number without the associated labels and code.
A key is just a long number. The AACS encryption key controversy was the subject of DCMA take downs because the key could be used to strip DRM, not because it was a number.
The level of creativity needed for copyright is minimal. A key pair is generated by machine, but at the request of a human according to parameters selected by the human. That is likely enough.