The wording is confusing, but I believe the Zhengzhou International Land Port is 50sqkm, not the factory. That also fits the numbers they're giving [1]: "Zhengzhou International Land Port Project announced ——total area of around 50 square kilometers", and that includes a lot of "open-air warehouse" (parking lot). It's still massive, but not quite as crazy.

1: https://www.zzhkgq.gov.cn/2024/01-28/2944537.html

Agreed, the factories clearly aren't the same size as Manhattan.