I think another divide when it comes to “social media” is the idea of following someone.
Facebook, Instagram, Twitter, etc let me follow people (or brands).
Reddit however isn’t about people or brands (and yes I’m away they added that feature, it’s stupid), it’s about topics.
Looking at Mastodon, it is also designed to follow people. They do however have the option to follow hashtags, which as a Lemmy user is something I like.
Similarly as a Lemmy user I don’t care who any of you are. I’m not following anyone in this thread. We could interact every day or we could interact once a year, I don’t care who you are and I like that.
Also, I don’t care if you follow me. I’d prefer if you didn’t. I do have an opinion to share, and I do want people to read it. Is that “social media”?
As other folks have pointed out, this is all more similar to Internet forums. Are those “social media”? I would argue they are not, but if you stretch the definition far enough… I guess?