I don't have Facebook. I don't have Twitter. I don't even have Instagram, or TikTok. I stay away from all kinds of social media, aside from Telegram to chat with my friends, and it's been this way for the last 10 or so years... and boy do I get confirmation that I made a very good choice very, very often.
How is hacker news and likes of reddit or even slashdot not a social media. In some ways reddit is much worse (echo chamber) than twitter.
I'd say to qualify as social media you need to make the experience about connecting people with each other or with groups, and finding people to connect with. Things like Instagram, TikTok, Facebook and Twitter are all definitely social media.
A site that just posts news headlines that people comment on is not really social media IMHO.