You're right that the existence of PyPI doesn't mean everyone is forced to link back to it, but damn it would make a lot of stuff a hell of a lot easier if it did. I've been bitten by Debian packages being years out of date, I've seen packages modified by maintainers in ways that are poorly documented and useful for Debian users rather than Python ecosystem participants.
I've managed to work my way out of that now and would never go back to that world if I can help it as the trade of reduced engineering quality (along various axes) for increased "freedom" is not one that I value (personally, or at work). So I can really empathise with this persons position.
I think they handled it poorly, communicated poorly, came to the wrong conclusions, and left the discussion in a bad place, but all of that just screams frustration to me, and I can understand where it comes from.