Yes, it's the leftover from making butter with cultured cream. Most of the buttermilk you buy these days isn't such a byproduct though—it's fermented in mass-production. So ironically, her statement would make more sense if applied to grocery-store-not-farm-fresh buttermilk. Don't know if there's a point beyond a truly pathetic inferiority complex. Perhaps signalling that even rural areas won't be a safe redoubt for Whites?