Yea in the same reddit thread someone asked "Well how did they migrate from England to America after the apocalypse?" and the response was "Because Prydwen" so once again using Bethesda's "lore" to justify more Bethesda "lore." If we're going to go down that road than pretty much anything goes for Fallout - there will be Ancient Aliens, Kid in the Fridge, all sorts of new lazy and carefree "lore" that has nothing to do with Fallout or a cohesive universe.
Lou Tenant had a British accent, but that was one character (a super mutant). Fallout 4 is basically a melting pot of various accents as though people are freely traveling from Europe and Russia to America. It doesn't make sense.