When southern people say y'all to one person, they're really addressing you and your family (even though you might be the only one there.) If I ask "how y'all doing?" I want to know how you and yours are doing.
I just want people to stop asking me how I'm doing if they don't care.
It took me an embarrassingly long time to figure out that "How's it going" is a greeting, not an interrogative, and I want that change undone forever.
I just use "Howdy".
That's something those western southerners told me. I don't know if a linguist would agree, but that seems to be the understanding of some actual language users...
All I know is that there is a second boundary somewhere through TX, NM, and AZ, because I've never met a native Californian who would say "y'all" non ironically.