Please explain: why is comparing the PISA test results an apples and oranges exercise?
Because there is a worldwide pattern of difference by ethnic groups. Thus, if a country is composed exclusively or almost so of a high scoring group, it will have high scores. If a country is a mix of groups, it is likely to be in the middle, etc.
This is not politically correct, but alas, it is true.
The racial/ethnic demographics are skewed in the sampling. The average IQ for ethnic Chinese is 110. The Shanghai students are likely 100% ethnic Chinese. The "American" group is going to be a mix of racial/ethnic groups. The mix has a likely "average" IQ of 100. The comparison isn't valid. Select just the racial/ethnic Chinese from the American population if you want to compare apples to apples.