Those are statements about auto-formalization and the NL proof. They're saying that further work needs to be done on verifying whether the Lean and NL proofs are equivalent, which is completely valid. But they're not disputing that the Lean formalization is a correct statement of the Millennium Prize problem. You can see in the link I provided (and the original pull request) that it was written by humans, reviewed by human experts, and is completely independent of the OpenAI effort.