Does being 'humble/giving' in the researcher's context reflect the personalities of individuals in the researched countries?
I agree, volunteering ones time has never been Tanzanians strong suit, but that doesn't exactly say that Tanzanians are 'mean' in the true meaning of the word.
One just need to visit Tanzania and find out the truth. I will be willing to bet my neck that if you pick any day of the week and hit the street of any Tanzanian region (as opposed to any other country in Africa and the world, for that matter) posing as someone with a need, Tanzanians will be more than willing to be of any help/assistance.