Why do some black people believe that black Africans founded China and many Native American Civilizations such as the Olmec?

 

The original modern peoples in Eurasia interbred with the Neanderthals in the Middle East, then later with other hominids and the Denisovan in Eastern, Southern Asia. All Eurasians carry ancient Neanderthal DNA. 

 

Olmecs were indigenous Asians carrying indigenous Asian Haplogroups.

Olmec - Wikipedia

Mandal man of China dated 12 000 - 10 000 years ago:

Early Hominids in China:

Homo-Erectus Pekinensis

Ancient Native American recreated:

Kennewick Man found in Washington and dated 9000 years

12 000 year old Naia found in Mexico and recreated