For me what puts Hacker News in the same bucket as Twitter, Reddit, or Facebook is that it’s a constantly refreshing feed of content that requires very little choice or initiative on my end to access. It’s always here, always novel, and I don’t have to think from a blank slate to figure out what I want to read, I just come and pick from the menu that’s been put in front of me.

I can contribute and participate actively by doing critical thinking and leaving comments but I can also read passively and barely even think my own thoughts. For me that passive version is the default.

I agree that social media is not the most accurate term. I wonder what a good alternative would be. “Mindless feed reading” could refer to the act of consuming it.

You are being pedantic. Yes, if you're in a group and exchange discussions which are low-effort(memes) and high-dopamine(outrageous views) you are in the cycle.