The myth in this article is that a per capita average of income tells you anything about the condition of the poor. Many countries can raise that number significantly by simply asking Mr. Gates to visit for a day.
To address your snide side comment... Gates visiting would not change the per Capita GDP. GDP and per capita GDP is not calculated that way.
GDP = private consumption + gross investment + government spending + (exports − imports)
and
Per Capita GDP = GDP / Population
Visiting rich foreigners, or even rich expats who just reside somewhere but have no business activity do not change GDP except through their local spending (private consumption).
Read http://en.wikipedia.org/wiki/GDP for more info.