Maybe it's obvious from some other source, but the judgement description on Justia doesn't really seem to support that. My impression (not a lawyer, haven't done any significant research into the case beyond reading provided links, etc) was that the case was determined based on non-literal copying. If I see the source code for an application and then write my own application that doesn't share code, but does share the overall structure and makes the same design choices, there's an argument that I plagiarised the original software just as much as if I took a novel and rewrote the same story in my own words.
That doesn't seem to be true of an API. A program is the embodiment of an idea, ie an expression - the same program can usually be written in a myriad of ways. An API is a functional description of how to interact with that program - there's no way to reimplement that API without it looking identical. An API may require significant design, but design is usually protected by patent law rather than copyright law.
So really the case hinges on whether an API is an expression or merely an idea. If the former, then it's copyrightable. If the latter, it's not. Johnson v. Phoenix doesn't seem to give us any insight into that.
That doesn't seem to be true of an API. A program is the embodiment of an idea, ie an expression - the same program can usually be written in a myriad of ways. An API is a functional description of how to interact with that program - there's no way to reimplement that API without it looking identical. An API may require significant design, but design is usually protected by patent law rather than copyright law.
So really the case hinges on whether an API is an expression or merely an idea. If the former, then it's copyrightable. If the latter, it's not. Johnson v. Phoenix doesn't seem to give us any insight into that.