I've never been that far to the south but lately I've been reading and watching those novels and movies.
The prevalent idea is: in this world (Texas?) you are alone, nobody gives a cr*p about you, do not trust anyone because they'll take advantage of you, ridicule and mock you. The world (or maybe only Texas?) is an inhospitable, inhuman, Darwinist place.
Like how New Yorkers are rude but not mean. I remember a culture shock moment the first time I went to a bagel shop there and the scowling woman at the counter said "whaddya want?!" It took me a moment to figure out that she meant "what would you like to order?" and not "what the fuck are you doing here?"
I am also confused though as I have family in Texas and they are polite and pretty happy but not sure I would describe them as kind.
I dunno. I think of Polite as the superficial, outward forms; and Kind or caring as the actual giving a fuck, never really considered what Nice means to me. But I do think the outward forms, being able to put a person at ease, hospitality, is a form of caring in a way, you have to be in tune with people to accomplish it, and it is a good skill to have. But you don't have to literally care about them to do it, if that makes sense.