Well, nooo, Botswana is NOT the most successful African country; Equatorial Guinea fits that billing followed by Seychelles. Your link is rather old. A lot can change in a decade. Besides The IMF and WB are NOT benevolent agencies. Perhaps you should check the source of the report in your link to see if it originates from the IMF or the Word Bank.
Another thing, the GDP per capita does not reflect the individual citizen's standard of living. The GDP is a hypothetical whereas all income produced from the sale of goods and services is equally distributed to every citizen.. The people of Botswana could be mired in poverty but on paper, the IMF makes everything seem rosy!
"Several aid programmes run by the IMF and World Bank have been terminated due to corruption and mismanagement. Because of vast oil revenues, the country is no longer qualified to concessional financing, but the government has been trying to agree with the World Bank and IMF on a "shadow" fiscal management program."
http://epri.org.za/wp-content/uploads/2011/03/16-Equatorial-Guinea.pdf
Seems like IMF and World Bank Aid helped build up the economy of Equatorial Guinea as well, however, they are so corrupt at the moment the IMF and World Banks have cancelled their financing to the country, despite objections from the government of Equatorial Guinea.
Any success you see in Africa, the IMF and World Bank had a hand in it. They aren't the evil organization you make them out to be. They are a financial body that aids struggling nations and promotes fiscal discipline to sustain long term economic growth.