I agree with your general sentiment and was initially inclined to make the comment more verbose and not include the URL; I would certainly not be content with just a URL. Still, in this case I would consider it a fair compromise, primarily because the inclusion of the URL is non-essential but value-adding. That is, it explains more, but the two important points—the purpose of the code and the reason for the number 3—are captured by the lines above, but the blog post adds more information which could potentially be of use later. Furthermore, the author of the code is the author of the blog post, which increases the probability of its survival.
