To me, Reddit is clearly an example of social media, and less clearly a social network. Compared to Facebook or LinkedIn, for example, it has much less focus on the network aspect, connecting individual users, and a much larger focus on what is being posted. On larger subreddits, most interactions are with random strangers, rather than people you have some close relation to.

That being said, I do think the ability to create small communities and organize that way could just be considered a different way of modeling connections. Rather than peer-to-peer links, you have topic groups as the primary structure.

There's definitely a spectrum, though, and I would be willing to accept it if somebody made the argument that Reddit wasn't a social network.