I'm not sure Joel wrote about this to brag; at the very least, he wrote about this because it made for an interesting / relevant entry for his monthly Inc.com article.

I agree that it might come off a bit as preening, but to be fair Joel's column hasn't stayed away from mistakes and bad decisions he's made as well. As such I take the tone as being closer to "this is what I've done and why I've done it" than "look at this awesome thing I did".