If LLM-generated code isn't considered a derivative work of the original, then whether the author was licensed to use the code doesn't matter. But I'm sure the courts will rule in favor of your view regardless. Laundering GPL is in corps' interest and laundering their code is not.
I'm not sure why people are clinging to some fuzzy and stretched out notion of copyright and the GPL in a particular. LLM's do NOT just copy code, with the right prompting, they generate entirely new code which can produce the same results as already existing code - GPLed or not.
If copyright is extended to cover such cases we'll have to become all lawyers and do nothing but sue each other because the fuzziness of it will make it impossible to reject any case, no matter how frivolous or irrelevant.