I like to sing in French, Eat cat food, Throw rocks at boys, And live my life according to a cookie.
Modern China was founded with communist principles in mind. But after Deng Xiaoping took power, he decided to move China toward a more capitalistic economy. But the Communist Party still rules China and therefore they still are labelled “communist”. Similarly, the US isn’t completely capitalistic because there are government regulations and also government-owned businesses (such as the post office).
It’s really a label more than anything else.
EDIT: Another thing to point out is that a lot of those “billion dollar companies” are actually owned/operated by the Chinese government. For example: Industrial and Commercial Bank of China. They have branches in the US now too.