People often ask why Africa is so poor, and immediately assume the legacies of imperialism and colonialism are to blame despite the fact that the wheel hadn't even been invented in some parts of Africa by the 1880s.

The colonization of Africa started a century before 1880, that example does absolutely nothing to support your claim. Even then, why would it matter if a population among the African race is technologically less advanced than the rest of the African race? How would that imply that the entire African race is technologically behind? Further, technology isn't invented that many times. For the most part it just spreads from one population to another. All you can prove with that example is that this population is isolated. Even further, it is by no means an obligation of a human to be technologically advanced. Though unpopular, if a society is happy as horticulturists or pastoralists, why demand them to become agriculturists?