In short there are differences, but they are not enough to account for there being no females or very few on most of the teams. That suggests that selection for the teams is either not based purely on merit, or there is some issue preventing more girls studying mathematics to the highest levels.
Should of read your own link, it was literally the entire second paragraph.:
In a 2008 study paid for by the National Science Foundation in the United States, researchers found that "girls perform as well as boys on standardized math tests. Although 20 years ago, high school boys performed better than girls in math, the researchers found that is no longer the case. The reason, they said, is simple: Girls used to take fewer advanced math courses than boys, but now they are taking just as many." However, the study indicated that, while on average boys and girls performed similarly, boys were overrepresented among the very best performers as well as among the very worst.
Boys have a larger variance in their scores than girls, so if you are trying to form a team of the very best of math(s) students it will most likely have a majority of boys if not be exclusively boys. And it is not a matter of only boys taking higher studies in math, as the third sentance explicitly calls out that girls are taking higher math courses as well. So no, there is no gender driven discrimination going on here, It is just a reflection of the team members performance. That you simply don't like it or feel threatened by it is irrelevant.