Saying that on average, women prefer working in people oriented roles whereas men prefer working in mechanical/technical roles is not sexist, because this is a fact supported by real evidence.
The author's point about societies with the most gender equity having bigger gender gaps really drives this point home. In societies where there is gender equity, people aren't compelled to behave a certain way and instead gravitate towards the roles they really want to take.
Real, verifiable, reproducible truths are not sexist or racist. They are truths. The fact that the https://en.wikipedia.org/wiki/Kalenjin_people#Sport dominate sprinting is supported by empirical evidence and also science.
So to be clear, racism and sexism are terms used to describe prejudices, lies and falsehoods about a gender or race. These terms shouldn't be used to describe real, empirically shown gender or race differences.
We as humans are all equal in worth, but that doesn't mean we are all the same.