You're right that these are the same story, and that's the criterion we apply, even if the articles are different.
However, the earlier one didn't get significant attention, so it's not a dupe in the sense that we would downweight the later post. We should merge the threads though.
Edit: since the other article has a bit more background and was submitted earlier, I've merged the comments thither. Thanks!
It's the same news event, but it's not the same article. Perhaps one is written better, or is somehow more appealing to HN? Who knows. Not sure if "materially identical" would account for that.