On HN, an article doesn't count as a dupe if it hasn't had significant attention yet. One user isn't allowed to repost the same article more than a small number of times (see https://news.ycombinator.com/newsfaq.html), but when the same article is posted by many different submitters, that's often an indication that it's interesting. Because of that, we invited Yuval_Halevi to repost it, since he was the first user to submit it in the first place. Invited reposts get put in the second-chance pool (described at https://news.ycombinator.com/item?id=11662380), which is why this one made it to the front page.