Relative economic standing != absolute economic standing.

Statistical measures of poverty are set in terms of being able to afford the basic necessities of life, such as food, housing, medical care, transport, education and communications. Relative standing is irrelevant.

Further, having 10 times more income (or wealth) than subsistence farmer in sub-Saharan Africa is meaningless if your cost of living is 1000 times higher than that of a subsistence farmer in sub-Saharan Africa. Poor Americans aren't paying sub-Saharan African prices; they're paying American prices, and that means their income does not go very far.