this is an example of the saying "figures don't lie, but liars figure."
It says it's based on the percentage increase in NUMBER of people living in impoverished areas. Well, guess what. The South had increased in population, while the Midwest and Northeast populations have either been stagnant or shrunk.
Thus since the overall population of the South had increased more, it would stand to reason that we would have the biggest increase in population in all areas, those impoverished and those not. It's a backhanded way of saying "newsflash, people of all types are fleeing the north for the warmer climates of the south."