Right, and I'm not saying it's absolutely definitive, or even my own conception of this distinction. However, if someone personally defines it that way for themselves, I think it's valid.
I define it this way. Social media centers around having a social identity that others engage with. I've been on smaller forums where I recognized every user name and knew their individual personalities, which is probably pretty close to social media. But most large forums are basically anonymous, and you don't engage with the user so much as you engage with the discussion.
If you just define "social media" as media which involves others, then all media besides a private personal journal is ultimately social.
Eh. I feel like people are choosing to change the definition so they can feel better about themselves. They aren't the unwashed masses on Facebook or other "social media", they are enlightened thinkers who use "forums" to converse instead.
The change in definition seems to be done specifically so people can say they are better than others.
Maybe....but they also aren't getting the real world "clout" that they are getting (or think they are getting) from real identity posturing and curated profiles. I'm not saying you're wrong, necessarily. Just that there's two types of arrogance at play here.