I pointed out a dupe, which is an ordinary, everyday thing done on HN. Nothing unusual there.

For some strange reason, interestica (and now you) chose to argue with me about it, futilely, as it turns out. I wasn't the one dying on a hill.

My understanding is that the moderators often see comments pointing out a dupe, or pointing out that an article title is missing a (YEAR), and such comments are helpful. Indeed, I've seen them thank some such comments. Moreover, it's also a signal to other readers of the submission.