So after all Nairobi doesn't contribute 60% of Gdp.

The measurement parameters by world bank and CRA are totally different, CRA used poverty levels while world bank used the GDP per capita e.g if Kiambu's GDP is Kes 10,000 with a a population of 100 people,the GDP per capita will be Kes.100.While if kajiado has a GDP of 10,000 with a population of 200,the GDP per capita will be 50.Hence Kiambu will be ranked richer than Kajiado yet in Kiambu it might be that only 5 people contributed to the kes. 10,000 while in Kajiado every person in the county contribiuted 50 to the GDP

In the eyes of WB, Kiambu county is the richest because it has the highest GDP per capita but in the eyes of CRA Kiambu county is the poorest of the two because majority(95 people) of the people in kiambu are not involved in any economic activity thus no source of income and liveliood as compared to Kajiado where everyone is invovled in economic activity.

there are 3 kind of lies...lies, damned lies, and statistics

And what would you say about Nakuru @ 8.5 percent contribution?

Its true.
Have ever visited a place in Kiambu called Ndeiya? Its poorer and desolate than a manyatta in Turbi desert.