Listening to this again, I can't see this as racist. Even if Letitia has a certifiably Southern American accent, there's no reason she cannot be from Detroit.
What DOES bug me about this interaction is that the two just don't seem like they'd ever speak on cordial terms, at least not without A LOT of history of cooperation. There is a sense of history between them, but they still seem to be speaking out of their own worlds. Adam still speaks like a gruff and defensively, while Letitia speaks with an upbeat, open, almost pleasant attitude. Perhaps it can be seen as both of their defense mechanisms, but I just found it jarring.