Yeah, I think the article conflated a few points: I think the issue the author was having was that he thought that decentralized social networks were meant to be decentralized communication platforms, when they were meant to be decentralized content delivery platforms.

The problem isn't the decentralization, it's the choice of a goal. However, email, IRC, Matrix, etc all already exist, and are what the author wants, so I do see tbe article as a bit misguided.

I think what the author meant to say was "I thought ActivityPub was meant to be more like Matrix, but it's not, and I'm sad about that".