I don't think he meant it like that at all. If he thought a girl couldn't teach you anything about integrals, he wouldn't have asked for help.

I think he used it as an example to show that the cultural distinction in his school between the genders when it came to math weren't enormous. Had there been a clear culture of math as an all-boys-no-girls subject, that exchange (were he as a boy asked a girl for help) would never have happened.

It is an example used to convey that it wasn't common for boys to think a girl couldn't teach you anything about integrals.