So, _London_ is further north than anywhere in the contiguous United States. But obviously much warmer than a lot of it, particularly in winter (London rarely gets far below 0 Celsius). Latitude very much isn’t everything.
If you look at the prevailing winds off of the eastern atlantic, it looks a lot like Southern Sweden gets the same air that London does. Plus there's a couple of considerable lakes along that path, so grapes do seem plausible.
