You know authors and their egos: they just love to write about writing. So, it's never a huge surprise when writing is a theme of a book. In the first chapter, Steinbeck sets up a big metaphor between collecting sea life and trying to write about life in Cannery Row, and he's not afraid to get gross: the stories are worms, the resulting books are like embalmed cats and frogs, and so on. Writing in Cannery Row isn't something that artistes do with nice pens at fancy desks. It's a job, like working at the cannery or collecting sea worms. But probably less smelly than either.
If writing is like collecting sea life, then Doc is like the writer, making stories out of life. And like a writer, he seems to stand a little apart from the rest of Cannery Row.
Steinbeck's treatment of writing suggests that Cannery Row is leaching the life out of the real Cannery Row. Writing about something inevitably changes it, and to change Cannery Row would kill it.