You are correct as usual.
Some customs and mores associated with being Southern are simply old Anglo-Scots-Irish-Huguenot leftovers that faded elsewhere and stayed on in the more homogenous and provincial South.
Unfortunately, that is changing here as well now.
Well, I usually am; correct, that is. LOL
That " sleep tight " stuff, is VERY New England, BTW. It's also VERY New York ! As a child, I was told that, every night. I said it to my daughter too. Heck, I still do ! LOL