I am French and I've lived both in "province" (means not in Paris...) and in Paris, and I don't think that's particulary accurate to say that people are much friendlier in province. I've met friendly people both in Paris and in "province" as well as unfriendly ones...

In my opinion, it's just a way of reenforcing this dichotomy between Paris and "province" (and this word is also part of that scheme).