"Calm down" is patronizing; "political correctness police" is pejorative. This is language one uses not when trying to have a civil, substantive discussion, but when trying to skewer an adversary.
I called it a personal attack because it's needlessly personal: it implies that the other person is an overwrought ("calm down") fanatical ("political correctness") bully ("police"). If that doesn't meet your definition of "personal attack", I'm happy not to quibble. Either way, though, it doesn't meet Hacker News' definition of civil, substantive discussion, and therefore is inappropriate here.
I called it a personal attack because it's needlessly personal: it implies that the other person is an overwrought ("calm down") fanatical ("political correctness") bully ("police"). If that doesn't meet your definition of "personal attack", I'm happy not to quibble. Either way, though, it doesn't meet Hacker News' definition of civil, substantive discussion, and therefore is inappropriate here.