"Hack" related to writing has been around much longer. IIRC, Byron described himself this way. The article here concerns the tech sense only.
Also, in the case of a writer the noun isn't "hacker" but just "hack".
Edit: can't find the reference in Byron. I am reminded, though, that a "hack" used to refer to an old or low-quality horse that would be let out for hire. Perhaps it got applied to writers from there.