Or whether East Asian IQ of 105 and the relative strength of East Asians in math means that even if there is a sex difference in math among East Asians, the overall level of math ability is high enough that girls do well.
Better than their males, in fact.
China is a country where the preference for males is strong enough that the sex ratio is skewed by sex-selective abortion. "Gender equity" may be worth pursuing for its own sake, but I don't think it explains differences in the math achievement gap by sex across countries.
It certainly can't explain the difference if you're going to treat a math achievement gap as an a priori assumption in the face of data that directly contradicts it.
China's sociological gender selection could be an explanation for its results, but the same cannot apply to Singapore or Chinese Taipei (Taiwan). It also wouldn't explain the results for some of the varied cultures that demonstrated superior math performance for females, such as Sweden, Qatar, and Trinidad and Tobago.
