It doesn’t matter. It’s likely had access to the knowledge of somebody who worked on that source code.

I have worked at companies that have done clean-room implementations. I was not permitted to look at their source or interact with those teams, because I had been exposed to the source of what they were re-implementing in a prior job.

As a human with a mushy brain I was never going to remember the source, but the fact I had been proximate to it was enough to lock me out. You have no idea what the LLM trained on, so you can’t prove a LLM derived clone is a “clean-room” implementation.