The important part is the linked GitHub comment from the primary maintainer (and owner) of the Nitter project. To save readers a click
Guest accounts have been removed, they weren't just led to believe that. With real accounts getting rate limited immediately and likely banned, I don't see any path forward for Nitter.
I would say that Nitter as a whole is not owned by anyone, that person is the owner of one of the Nitter instances, in addition to being the primary maintainer of the project as you correctly stated.
I agree with the second part of your comment about all instances being in danger. It is unfortunately a common problem faced by many privacy-respecting frontends (Nitter, Libreddit, Proxigram, Piped etc)
It's also factually incorrect to suppose that this person owns the Nitter project, too. There's no CLA so the copyright is held in common by all of the contributors. Free software projects don't have owners, they have maintainers, and the maintainers are a social construction rather than a matter of property law.
But zdeus is the 'owner' of the nitter project on Github. That's their official word for it, even though it doesn't necessarily have anything to do with the legal concept of (copyright) ownership.
And then there's 'owner' in the software dev sense, i.e. the one that ultimately decides which direction the project takes, what patches to merge etc. is sometimes referred to as "product owner".
This seems factually incorrect, but in a nuanced way.
The copyright owner of a code is the one listed as such. In cases of multiple contributors, each owns the copyright to their individual contributions. For projects with shared contributions, it's more accurate to say each necessary part has its own copyright owner, rather than a common ownership.
Free software projects do have copyright owners, which can be entities like non-profits or companies. This ownership is crucial for legal standing in copyright infringement cases, except for public domain code, which isn't copyrighted.
It's wise to have a Contributing.md or similar, stating that contributors affirm their creation is original, free from patent issues, and they agree to license their contribution under the project's terms.
Without such agreements, there's a risk contributors might withdraw their code, claiming it wasn't licensed under the project's terms, potentially leaving gaps in the project.
Simply hosting code on a site with a common license doesn't automatically apply that license to your code unless you explicitly agree to it.
> the maintainers are a social construction rather than a matter of property law.
Property law itself is a social construction of exactly the same kind.
A single person or group owning a FLOSS project is also a typical, almost universal case. There's always the person or team, and the canonical repository, that represents what "Emacs" is, or what "sr.ht" is, etc. In practice, for everything except legal issues, this is the same as legal ownership.
The way I interpret this comment is that all public Nitter instances are at risk of becoming inoperable (at their current scale).