Strongly disagree.
Social media is where one shares ones social life (it's in the name!). HN, like many other sites dating back to the days of USENET, is a subject discussion forum; in HN case, a technical / IT discussion forum.
Granted, there are sometimes crossovers between the two, but HN certainy isn't one of them.
Oh, maybe it's not exactly like facebook or Twitter, but it ticks so many other boxes.
I could list many, and argue about them (arguing: another staple of social media), but the most important to me is that HN is effectively a procrastination tool, and it's associated with that mental "fix" of instant gratification.
It's different from facebook in that HN is more heavily moderated and more focused, but other than that, it triggers the same kind of (bad) habits, at least in my case.
Reddit, on the other hand, is a huge time sink (some good, some bad, I read an awful lot of short fiction on Reddit, and I consider that a positive).
I can think of dozens upon dozens of posts that were useful over the years! In a way HN has reduced the amount of networking I have had to do in order to see what people are interested are in, as they are posted here!
