Depends on the definition.

Nationality, language, cultural, ...
A type of temper doesn't depend on where you're from but more to a mix of genetics, upbringing, cultural, life experiences, ... so that claim is to say it like a psychologist would say: total BS.
Also in the north people have
in general more a habit of strait out saying what they mean to your face. In cultures where this isn't done, it can be seen as rude or bad tempered. It's all in the eyes of the beholder.