Two other posts from today: * Ask HN: Why does a busy man build a shed? ( https://news.ycombinator.com/item?id=29767682 ) * Why I Live In a Shed ( https://news.ycombinator.com/item?id=29762145 ) Does HN have some kind of mechanism that promotes posts with similar keywords?
I've noticed this happening as well, and the explanation that I've stuck with is that the follow-up posts are posted by readers who recognize a similar article they've previously read that's deserving of a (re)post on HN.
Another easy one to spot: there's sometimes clusters of articles from the same site if it's not a well-known one - people look around the site, find other good stuff and submit that too.