1. There are a lot more people/km^2 in Central Africa
2. Tibet is the lightest shade
3. Countries are not uniformly shaded. The US has all colors in various regions.
1. The African jungle/Serengeti are not densely populated. Besides, spend five minutes in an average Siberian village and it's immediately obvious this is nor a wealthy place.
2. Both Tibet and Siberia are desperately poor and sparse locales. One is better than the other, but not by much.
3. The map is running on the assumption that GDP Per Capita is uniform within the borders of a country, when this is definitely not the case. Suppose that a given country has a per capita GDP of $15000, with a rich half of $20000 and a poor half of $10000. Suppose that the country's population is evenly distributed. Under the given map, the whole country will be given a single shade, which is factually incorrect. In China, Shanghai's Per Capita GDP is 7.56 times that of Guizhou (the poorest province). This map is assuming that everyone in China/India/Russia/etc has an equal GDP per capita, which cannot be further than the truth.