He's a writer and is experiencing the difficulties of his work and how it effects his emotional well being. It shouldn't then really surprise that he sees a strong connection between his work as a writer and the depressions he has. That doesn't mean he's telling an objective truth about a writer's life, but he's telling a subjective "truth" of his life as a writer, and sometimes these subjective "truths" can tell you quite a bit about life.
Sometimes the HN crowd can get quite a bit annoying with its scientific thinking, because it's not always the appropiate method, and sometimes a single person can tell you more about a certain aspect of the world then any kind of scientific study.
I'm certainly not arguing against the scientific method, but to apply it in a reasonable way.