Reddit is considered a social network?
Mine would be a system connecting multiple entities for the purpose of socializing... or something like that.
So I'd say yes, imo.
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.
Reddit exposed you to new ideas and people. Some good and mostly bad but it is much more "Social" in action.
They are completely redesigning and rewriting the website from scratch with the objective of turning into an actual social network. Look what the new user profiles look like: https://www.reddit.com/user/spladug
Microblogging platform that allows your to embed images and video. Has the same harassment, hate and political controversies that Twitter has. The only difference is community moderation, which can be seen as good or bad. It will be interesting what community moderation occurs after its a public company.