In this case, Black box mean you don't reveal your protocol works and people don't know anything about your protocol. All they know are it's input and output.
Alright, so that's not a black box protocol, since I already revealed several aspects of it on my OP. And calling it a string is not an oversimplification, it's a statement of fact, since it
IS, undoubtedly (albeit a long one), a string.