I noticed the same thing with gwern posts. I assume what happens is HNers see a random article on the front page, like it, and start browsing the sites archives for other interesting articles. Then they submit them to HN and the process repeats itself.
I’ve noticed it becomes relatively easy to anticipate which articles will reach the front page once I’ve started reading the trending sites. However, I wonder whether there’s any way to anticipate which sites will begin to trend on the front page. My first instinct is that it’s just a matter of circumstance, of one person sharing one article from a non-trending site that trends on the front page. In practice, however, it’s hard for me to believe that such a small event could decide whether or not a story gets covered by a more mainstream site after a journalist finds it—I’ve been seeing quite a few references to Hacker News articles as of late in mainstream news articles. It could be that Hacker News really is the initial component in starting news trends.
Gwern was for a while submitting one article to HN every week and most of them seemed to make the front page. Maybe that's what you're recalling? It was some time ago, though.
