[incompatible]

You are free to pick a different definition. "Permits arguing and procrastination" would make it a pretty big category, including all online forum and chat systems back to the Usenet / BBS and maybe CompuServe / Prodigy days (I don't know enough about the last two).

[MattRix]

uh yeah, those things are absolutely social media as well

[incompatible]

Usenet seemed more social than HN, as I remember it from the 1990s. You'd go back to the same groups, and see the same people posting. On HN, I don't usually see any name I remember.

[the_af]

I regularly see names I remember on HN: tptacek, pron, dragonwriter, lmm, coldtea, etc.

It's not exactly the same as contacts on Facebook, though it's closer to Reddit. Definitely social media.