I suspect that the link: operator doesn't work well (or at all) anymore, and that those results are only getting returned because the comments contain all the words in the URL (because someone invariably links to the FAQ). Other searches (to articles linked from http://news.ycombinator.com/best) come up empty:

http://www.google.com/search?q=link:https://github.com/blog/...

http://www.google.com/search?q=link:http://blog.instapaper.c...

http://www.google.com/search?q=link:http://mobile.nytimes.co...