It's possible that it considers Hacker News as a source of potential blog posts, which it seems to index very quickly. You probably just got really lucky.
It indexes Hacker News extremely quickly. In the few instances I've checked, new articles and comments were indexed in Google within minutes.
I'd imagine this makes our community a pretty heavy target for spammers.
Well, not as extremely. 16 minutes after your post I did a search for it and it was not in Google's index yet.