Maybe? When I see people talking about social media, they say stuff like Facebook, Twitter, TikTok, etc. It's not hard to extend that to say, Tumblr, which Cohost borrowed a lot from, for example. Though I will admit, I've never really heard of a Discord or Reddit "influencer"...
So that would make Reddit social media, if I'm understanding correctly. I think not HN because everybody sees the same front page. I don't know if Discord is pushing personalized server suggestions yet.
HN is somewhere in the middle because the feed is shared instead of personalized, but it's still algorithmic and with global reach so I place it close to other social media.