Believable but at the same time might be just marketing, especially the last part. Call me cynical.
Of course, being informed about it may very well discourage some people from pursuing side projects. But then this comes down to whether you'd rather have developers continue with their side projects oblivious to the potential consequences of doing so.
My friend and fellow intern Tad fielded the return call from the guy who had the issue, and while I didn't speak to the customer myself, I believe Tad's account. It makes sense to me that Bill's answer wasn't quite correct, he did just essentially read the customer the first result from querying the error message on the Knowledge Base.
I mean it's possible, but it's also possible it's just a nice story.
Those details were fictionalized by the author. Everyone who wasn't actively on a call at the time new all about Bill's call, because we were all standing around my cube when it happened. Not long after the call was over our entire team knew all about the call, what the issue was, and how Bill handled it. If I recall it was about an obscure linker error message.