I don't know about that. Is any web site that has user comments social media now? That seems an overly broad definition.

HN isn't particularly social as far as I can see. I don't have a network of friends. It doesn't facilitate personal connections or groups.

As a quick check, here's the first definition from a google search of social media:

"websites and applications that enable users to create and share content or to participate in social networking."

I was surprised by the "or".

https://www.google.com/search?q=define%3Asocial+media&oq=def...

Your definition of social networking uses itself. That’s not a great definition…

Were 90s newsgroups and BBS social media?

Yes

No, they were before social media was a thing. Social media has an implicit social network behind it and profiles where you can post information, not necessarily in a forum.

HN has none of these features. Neither do BBS message boards.