>What are the clear criteria that make something social media
I have no idea why people are making some mysterious deep question out of this, wikipedia quite literally offers a definition[1]. Web 2.0 based platforms, user generated content, social networking including social mechanisms such as followers, groups and lists.
This doesn't apply to HN. You could randomly assign everyone a new name tomorrow and it wouldn't matter. Identity is virtually irrelevant here, there are no mechanisms to connect users to each other, there are no networks of people, users do not generate their own content and there is a criterion that what is discussed is of of public, not merely social or personal interest.
If some crash wiped out all HN users tomorrow and we'd all start over at zero almost nothing would change. If that happend on social media, like Instagram, the site would be dead. That's the social part.
> This doesn't apply to HN. You could randomly assign everyone a new name tomorrow and it wouldn't matter. Identity is virtually irrelevant here
This is wildly untrue. I follow specific people here and I recognize names all the time. It would be super confusing if some of the people I'm interested in hearing from completely different names. And comments are content. I read old threads all the time. If that all went away, a huge part of how I use this site would be gone.