Only by the loosest possible definition that would also encompass forums, IRC, game lobby chatrooms, etc. There's a clear and practical distinction between communities driven by a specific interest like this one and platforms like Xitter.
Saying that HN is social media is like saying that a taco is a sandwich.
Disagree. That's what HN and IRC fans tell themselves to draw an artificial distinction between networks they like and networks they don't. I don't see a huge meaningful difference except in scale and content breadth.