It's partly true; but depends where.
I cannot say for the northern part, for I never went there; but in the southern part like I said earlier tendencies vary from extreme-left in west and extreme-right in east; I went in two villages and had different points of view. If you go in Tarn-et-Garonne that is a department located in south-west you'll see great bastions that will vote left or extreme-left, and if you go in villages of Vaucluse, so in the east, you'll meet bastions of right and mostly extreme-right tendencies, the family I met there was limit neo-nazi and this didn't please me much to know such ideologies do persist in western european countries. So yeh, rural population tends to be extreme, but in both sides, depending of the place. And prejudices about immigrants are also found in great towns, may it be Paris or provincials like here in Toulouse, and some others.