Regular visitors knew each other after seeing the other users' posts, there are in-jokes, and it's not so different. I would say HN is less self-centered (we don't have unique avatars or signatures) than many old-school forums were. Friendships are less likely to be formed here.
And I ran a forum, over a decade ago, in which people from all locations/walks of life participated, and I met more than a handful of them in real life. I don't understand what point you're trying to make.
I don't know of any ills with social media that weren't present on forums for me. The difference seems to be one of scale.
I know my intention for joining both was the same (human connection over common interests).
[edit] and in this case the term is far more useful if it is not as expansive as you suggest. We’d just need another term, then, to describe the kind of thing people usually mean by “social media”.
Is the person (their face, their personality) more important, or the content of what they say is more important?
HN falls much closer to the "content" end of the spectrum.