Having been to Japan several times… and actually studying Japanese studies… I can see why you're saying this but it's very superficial. None of the southern "essence" that caused the split & war is there in Japan at this point. Or do you mean it's as if the South seceded, then proceeded to lose anyway due their policies being a natural disadvantage, and then developed, out-northing the North?
What is characteristic of "the American South" here?
Presumably the characteristic being referred to is superficial politeness mixed with racism or xenophobia.
When I lived in Japan and was asked "Why are you interested in Japan?", I used to respond "It is the only non-Western country(at the time) where I have seen an extremely high level of technical/economic development and it is interesting to see similiarities/differences". (This is of course, long long before the rise of modern China)
The society is based so strongly on group cohesion and de-emphasis of the individual, the experience of living there is very, very different than the West.
I think that this "deep cultural difference" is what the original comment was trying to get at. Sadly the reference point of "American South" ended up triggering a different (less useful) trajectory for the responses.