No disclosure for LLM-generated patch?

Copyright law isn't this simple. For one, it is established law that only humans can create copyrightable works and the copyright of the output of programs is based on the copyright of the input (if the input is sufficiently creative). Copyright in its current form is entirely based on "human supremacy" when it comes to capability of artistic expression, and so comparing examples where humans do something equivalent is not (in the current legal framework) actually legally equivalent. Maybe that will change in the future, but that is the current case law in the US AFAIK (and probably most other countries).

You could just as easily argue that LLMs produce something equivalent to a generative collage of all of their training data, which (given the current case law on programs and copyright) would mean that the copyright status of the training data would be transferred to the collage. You would thus need to make an argument for a fair use exemption for the output, which your example would not pass muster.

However, this is not the only issue at play here -- to submit code to Linux you need to sign the DCO, which the commit author did with their Signed-off-by line. However, none of the sections of the DCO can be applied to LLM-produced code, and so the Signed-off-by is invalid regardless of the legal questions about copyright and LLM code.