That's explicitly called out by miedzinski, the PR author, in the discussion [1]--although for some reason it's mentioned as PEP 512 but links to the same page you mentioned.
Reading through the Pull Request, it's nice to see such a civilised, courteous dialog between the submitter and maintainers (https://github.com/python/mypy/pull/2761). I can imagine (and have previously seen) many similar dialogs break down and resort to less errm... "empathetic"/productive comments. Guido++!
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[ 4.8 ms ] story [ 20.0 ms ] threadhttps://www.python.org/dev/peps/pep-0518/
[1] https://github.com/python/mypy/pull/2761