I encourage you to read the actual report on PISA results for the US. It is not just China but a number of Asian and European countries who outperform the State's on average score but also having a larger number of high performing students and a smaller number of low performing students.
Just over one-quarter (26%) of 15-year-olds in the United States do not reach the PISA baseline Level 2 of mathematics proficiency, at which level students begin to demonstrate the skills that will enable them to participate effectively and productively in life. This percentage is higher than the OECD average of 23% and has remained unchanged since 2003. By contrast, in Hong Kong- China, Korea, Shanghai-China and Singapore, 10% of students or fewer are poor performers in mathematics.
There is a lot of interesting detail in the report related to how results are impacted by immigration (accounts for 4 % of the variance) and other factors including motivation and advantage.
All samples have flaws but this is still interesting reading.
