Plagarism protection for source.
By your analysis, copyright protection wouldn't apply to any software source code, since that is clearly procedure, process, etc.
Clearly, that's not the case. You can't use this clause to shave off the API from source code and leave one protected and not the other.
In fact, this clause just says you can't use copyright to protect the idea or process or procedure. That others are free to implement the process or procedure expressed, just not in the same or substantially similar words. It's the same as the test for plagarism. It doesn't exclude the form of words used from protection. Google copied the form of words because they copied the files, not just the idea.