The SCOTUS decision in Oracle v. Google didn't rule on API copyrightability. It merely assumed that the code in question is copyrightable, then showed how it's still fair use even if so, thus making the first question irrelevant to the decision. And this is very much intentional; they spell it all out:
"Google’s petition for certiorari poses two questions. The first asks whether Java’s API is copyrightable. It asks us to examine two of the statutory provisions just mentioned, one that permits copyrighting computer programs and the other that forbids copyrighting, e.g., “process[es],” “system[s],” and “method[s] of operation.” Google believes that the API’s declaring code and organization fall into these latter categories and are expressly excluded from copyright protection. The second question asks us to determine whether Google’s use of the API was a “fair use.” Google believes that it was.
A holding for Google on either question presented would dispense with Oracle’s copyright claims. Given the rapidly changing technological, economic, and business-related circumstances, we believe we should not answer more than is necessary to resolve the parties’ dispute. We shall assume, but purely for argument’s sake, that the entire Sun Java API falls within the definition of that which can be copyrighted. We shall ask instead whether Google’s use of part of that API was a “fair use.” Unlike the Federal Circuit, we conclude that it was."
The tragic irony here is that the understanding of copyright that those that do not like Copilot put forth would indeed make things like Java's API copyrightable and to the obvious detriment of innovation.
I don't see how this is related. The question wrt Copilot can be distilled down to "what constitutes a derived work", but there's no doubt that the original source code that Copilot was trained on is copyrightable. Conversely, with Java APIs, there was no doubt that Google's use of them produced a derived work - the question was whether the original is copyrightable and/or whether that is fair use.
"Google’s petition for certiorari poses two questions. The first asks whether Java’s API is copyrightable. It asks us to examine two of the statutory provisions just mentioned, one that permits copyrighting computer programs and the other that forbids copyrighting, e.g., “process[es],” “system[s],” and “method[s] of operation.” Google believes that the API’s declaring code and organization fall into these latter categories and are expressly excluded from copyright protection. The second question asks us to determine whether Google’s use of the API was a “fair use.” Google believes that it was.
A holding for Google on either question presented would dispense with Oracle’s copyright claims. Given the rapidly changing technological, economic, and business-related circumstances, we believe we should not answer more than is necessary to resolve the parties’ dispute. We shall assume, but purely for argument’s sake, that the entire Sun Java API falls within the definition of that which can be copyrighted. We shall ask instead whether Google’s use of part of that API was a “fair use.” Unlike the Federal Circuit, we conclude that it was."