If there's a "the original" the LLM is copying then there's a problem.
If there isn't, then (b) works fine, the code is taken from the LLM with no preexisting license. And it would be very strange if a mix of (a) and (b) is a problem; almost any (b) code will need some (a) code to adapt it.
> the code is taken from the LLM with no preexisting license
That's not good enough to comply with (b). The code must be specifically covered by an open-source license, it's not enough for it to just not have a license.