I'd love for you to correct me on this, but I believe this is nonsense. The only places that discuss this are very dubious articles from infotainment-style blog

I'd love for you to correct me on this, but I believe this is nonsense. The only places that discuss this are very dubious articles from infotainment-style blogs, and I can't find anything to back this up on Wikipedia, let alone anything more reputable. IIRC, the element of truth that begets the lie here is that the Southern accent does have some elements in common with older British accents. But it's not clear whether those elements are retained from those old British accents, or whether they've simply been added into the accent later. And even then, we're talking about very specific features - I think the rhotic R is one of them? - and not the accent as a whole.