Fun fact: Zambia’s GDP per capita was greater than China’s in 1975. So there’s a parallel universe where a human rights conference in China gets cancelled because of Zambian influence.
I don't think there's a reasonable possible world where whatever government controls the land area of Zambia overtakes whatever government controls the land area of China in the long term, regardless of what the GDP per capita metrics specifically looked like in 1975. The discrepancies that make Chinese civilization more prone to being globally-influential than central African civilization (like "rice agriculture") are at least thousands of years old.
I don't think there's a reasonable possible world where whatever government controls the land area of Zambia overtakes whatever government controls the land area of China in the long term, regardless of what the GDP per capita metrics specifically looked like in 1975. The discrepancies that make Chinese civilization more prone to being globally-influential than central African civilization (like "rice agriculture") are at least thousands of years old.