Why does everyone just assume all the businesses talked about in the article are American? Obviously some of them were not. It seemed that they were focusing more on foreigners.

China does not have rule of law, full stop. They have a constitution that guarantees freedom of press, religion, and speech, and it is completely meaningless because they do not have rule of law. What this means is that Baidu can make most of its money on medical scams and porn while any foreign company would immediately be prosecuted for any small transgression. Whatever rules China makes up, its just for convenience, if they want to get you, they'll find something.