Well, how are you defining social media?

I feel like "user generated content conducted between specific users, tied to specific accounts, where users have one-to-one public conversations and those conversations are foregrounded as the site's content" is reasonable.

So, if that's my definition Wikis aren't social media and HN would be.

But I also feel like HN is just a flavor of Reddit, and I feel that most people understand Reddit to be "social media".

I could be worng about those feelings.