Neither IRC nor BBS* use algorithms to create feeds of third party content based on user preference, history and a network of subscribed accounts, but Youtube does. Forums can count, depending on their implementation - I don't think many people would argue that Reddit is social media, but it definitely suggests related content.

More to the point, "social media" is not as strictly defined as many people on HN want it to be, because social media features have crept into numerous platforms and applications over the years, so it really can be subjective.

* maybe some have, IDK.