Well, if you are looking at an API which’s license explicitly forbids copying, I would stay away from copying it.
While this case do give a precedent, it is much more about this specific case being a fair use according to the supreme court, than on whether APIs itself are copyrightable.
Also, given most programmers’ assumptions, I would not base much on that alone :D But IANAL, so do ask one, to be safe.
Given the countless and fundamental APIs that are typically used in any program, do you not think that is a Bad Thing?
Given that most programmers have assumed that to not be the case, it would be very bad for existing code at the very least.