My strong opinion on this. Their secret is trade, China manufactures, they build, they create, they need more raw material than ever and Africa has that. That's why they are in Africa, they are making these deals so they can get their raw materials. That's one.
Second, China was "poor" not too long, it's fresh in their mind, they know how a poor place can just transform, and they see that possibility in Africa. Plenty of those that didn't make it in China figure they can in Africa by leveraging their connection to China. So it's not just rich Chinese in Africa, there are just average Chinese folks who move to Africa and do trade import/export and build small businesses too. They see the possibility and potential. Americans don't see that in Africa, most people alive in America today didn't witness when the majority of America was "materialistic poor" like Africa is today. Which was about 100+yrs ago.