To remind those not familiar with the an old standard practice, for a remake of a product X to be "clean room" and avoid copyright issues, traditionally in the industry developers working it were required to never have seen X's source code.

My argument is that while you write that it was "only pointed" to the API, an LLM, who can recite over 90% of a book in its training set verbatim, would also have trained on the original code (and can have it in "mind").

So "pointing it to the API" doesn't mean it ONLY used the API in its implementation. Could very well have used whatever internal knowledge of the behavior and architecture and choices of the original code - regardless of if it recited or translated the original verbatim or not.

So when considering this, "AI was just pointed at the API" is a weaker claim than it appears to be.