My (non-lawyer) take on that is when they say "began with the assumption that the APIs may be copyrightable, and thus proceeded with a review of the four facto

My (non-lawyer) take on that is when they say "began with the assumption that the APIs may be copyrightable, and thus proceeded with a review of the four factors that contributed to fair use" is that they're not saying APIs are copyrightable and basically ignored that question because they ruled that even if they are copyrightable googles use would be fair use and oracle doesn't have a case. it's a fairly common method cases are resolved, you say "assuming the plaintiff claims are all true, do they actually have cause of action for a lawsuit?"