Yes and no. HN is definitely social, but there are no friends, no feeds, and no notifications, so it's unlike social media as most people understand the term.
If I skip HN for a day, there's a whole front page of articles that I'll probably never see, and never know that I missed.
Sorta...yes it is media as it is information transferred over a medium..but I think nerdponx is excluding this because its more 'social internet' than social media. With social media, you are like a company, with your brand, that you are trying to ensure looks good and shows good collaboration with other companies. With social internet, you are a human talking to other humans through technology.
If I skip HN for a day, there's a whole front page of articles that I'll probably never see, and never know that I missed.