It's true at last anecdotally. Related, there's a running joke in some subset of the industry about the types of exotic derivatives that are so complex and esoteric "only french banks" trade them.
IMO shows more which countries have programs to train top math schoolchildren to win in IMO. That's very different than producing professional mathematicians, which is more about universities and graduate schools.
In France, good students go to “classes prepas” for 2-3 years. It’s a period sort of between high school and university. I’m not sure if students are eligible to participate in IMO in this period. Perhaps someone else could clarify.
Regardless, France has a strong math culture. This is clearly seen in Fields Medals.
“It is estimated.” Doesn’t specify by whom nor if its even accurate. Kind of like “We are reporting that …”.