Describing his efforts to get the entry changed, he writes in the New Yorker that he was told by the "English Wikipedia Administrator" that he "was not a credible source".
This is what happens when people follow rules without knowing what the rules were for. I'd imagine the secondary sources rule was intended to eliminate articles which weren't noteworthy (no one else thought there was anything worth writing about) and to keep personal bias out of the articles (this is what so-and-so thought, but who knows what anyone else thought). Obviously, neither applied in this case (the author won several awards for writing, the book won several awards, and was made into a mainstream movie, so it's clearly noteworthy, and there's exactly one person who would know what inspired it, and he wouldn't be a secondary source, so what does it matter what anyone else presumes?), but hey, a rule's a rule, right?
Yes, I'm sure the rule was put in place for what seemed like a good reason, but leads to some absurd results. I learned about it from a story on On the Media, where they were talking about a law professor who tried to get Wikipedia to fix an article using the law itself, but was denied. For whatever reason, my work blocks On the Media's website, so I can't link, but its worth searching if you have a few minutes.
The Professor Versus Wikipedia Apparently, the secondary sources rule is only for perceived credibility. They want everyone to be able to have access to the sources used, and they assume primary sources will be unaccessible from the Web.