If he did it similar to what I did back then, then it is depending on the cloud infrastructure, even if you think such a thing does not exist. What I mean with that is how your service is structured, what database it uses, what storage solution, whether or not it runs on serverless functions. Not everything is just a docker container.
I believe reproducing his server COULD be challenging, because I did one myself in the past, and know that it is never as easy as you think it is. Even if you are perfectly familiar with all that, chances are that most of the audience are not, and might struggle with setting up such a server. Thus my statement about why I understand the author's comment.
I also don't see it as "centralizing multiplayer", as there is no official multiplayer, anyway. It is all voluntary work, and there is no obligation to share source code beyond license issues, which most probably don't apply here.
The concept presented is also not new or revolutionary, there have been multiple multiplayer solutions in the past, and even today. Both with closed and open source code distributions for client and server. None of them are perfect or even near being ready for prime-time, so if your fear is that somebody is locking people in here, I think you can relax: this one will not be the ultimate multiplayer solution either. After all, we've got radio-silence of almost a year until you showed up.