Do you consider HN Social Media?

Yes, why would you not?

Not in the sense of the common uses of Social Media. I see it as curious discussion of interesting topics with some guidelines to try to keep it from going off the rails most of the time.

Such guidelines do not exist in Social Media and Social Media sites use algorithms to try to increase engagement and advertising and additional use beyond-dystopian levels of tracking and psychological warfare against people. Social Media sites curate what people see based on their personality profile to steer public sentiment and beliefs.

I use HN as a news aggregator, where there is often great value in the comments. Another (mostly) aggregator site has fewer active posters and DM, so it feels "social" in the old fashioned sense. I have gotten to know people there.

IMO, Mega-sites are not social at all because the users are no more than pawns, and their contributions have no significance, (except for "celebrities" ), whereas at a smaller site, anyone can contribute real value, despite the site being mostly an aggregator.

I feel like there's a difference between interest-based forums and relationship-based social media.

On Facebook, you follow your friends and then you hear from them (and their connections) on various topics ranging from the interesting to the mundane to the toxic, and it's that social nature -- the back and forth among friends and acquaintances -- that gives it staying power. You're there because your friends are there, no matter what's being discussed.

On a forum like this (or Slashdot before it, or many subreddits) you don't necessarily care too much about who said something, just what topics are discussed. Yeah, maybe over time you'll start recognizing some of the names, but you're not really there for them. Just for the topics at hand. You're there because of the topics, whether or not you actually know anyone else there.

These difference lead to various dynamics. Facebook tends to break friendships more often than not (politics), or encourage creepy stalky behavior (photos-first) or "creator" content. Topics-based forums are topic-first discussions around a few things, and the people and presentation matter less.

But of course it's not that black and white... you have Twitter with both people and topics, 4chan with neither interesting people nor interesting topics, etc.

HN is more like a "message board". Beyond the simple "flag" and "upvote" mechanism, there doesn't appear to be any algorithm customized to each user. As a result, very high quality content tends to populate the top of the home page.

I personally enjoy filtering by New. A lot of original authors post their work and it's fun to interact directly with them, which is more difficult to do once a post has hundreds of comments.