I grew up in the South and ate at little hole in the wall BBQ places all the time. Never saw any outright discrimination. Many establishments were owned and and operated by black people. I must say cuisine is one of the few uniting features of the south. The racism is still there, but it is quieter, subtle, and behind closed doors most of the time. It’s very sneaky and many people miss it.
I’m sorry for your experience, that seems painful.
I’ve has the opposite. I grew up in the south as an underrepresented minority and I found the gas station / food shack food culture to be really inclusive and taking orders from anyone who had money.
Granted, I grew up after the civil rights act, so it was probably different under segregation.
I’ve only ever experienced “we don’t serve your kind around here” on tv and movies.