Learn about something new all the time.
My entire paternal family is native to, and still resides in, Mississippi, and I've never once, in my nearly 60 years of life, heard of Mississippi pot roast.
Maybe it talking referring to the river and not the state? That would explain it
Or do I put it in the same category as Nashville Hot Chicken, which I'd never heard of till about the past 10 years, or less, despite having moved to Nashville when I was 2 and living within a few hours of it since. Having quizzed anyone I grew up with we came to the same conclusion, it's a new invention since Nashville became a destination outside of those coming for country music. None of us get the bachelorette thing, but that's a whole other subject.....