How is HN not social media?
Otherwise discussion on the topic is impossible, as one can always respond with "yea well you're on HN aren't you?!"
I think it's a valid point to question what people mean when they say they're not on social media, yet are posting on HN.
HN has none of those. As a result, I don't consider it "social media", I consider it a specialty news aggregator that has a robust comment section.
Back when FB and the like were new, calling them "social media" was done to differentiate them from sites like HN.