> (uncountable) Applications or websites allowing users to share content and communicate with one another via the Internet.
and HN:
[x] is a website
[x] allowing users to share content
[x] allowing users communicate
[x] via the internet
Perhaps you should invent a new term for whatever you're talking about? Depending on what you want, I might suggest "algorithmic feeds" (actually that appears to be an extant term, but it might be what you want), or "multimedia social media" (to exclude pure-text sites like this).
Actually, that's a decent point; it should probably add something about being primarily focused on the user interactions. That is, Wikipedia isn't social media, but I'd hesitate to say that the talk pages aren't.
> Basically nobody outside of HN would consider HN social media if they saw it.
And on that point we definitely disagree, though I suppose I could ask around. What do you think makes it not?
Forums have been around longer than the WWW and are more about interacting with topics than with particular members. Some let you follow or PM someone, but that's not the primary function, and HN doesn't even have that. Some social sites have expanded to cover forum-like roles too, like Facebook (Pages).
But most people won't think that far. They'll see HN and say nah, this isn't social media.