I think of HN (And really, any other website driven by user-generated contented content like reddit and forums) to be social media but not a social network.

I consider social networks to be a subset of social media where the focus becomes following specific users and having a feed consist of posts made by specific users, whereas reddit has a feed consisting on posts on specific topics.

It's more of a "thought" network or an "idea" network than a social network. Unless I am super motivated to click through to your submissions and comments (and then back read the parent posts to understand).. most of the interaction is limited to threads. So this limits any attempts to curate a theme or push a dominate ideology.