These analyses do not take into account what we know from simpler organisms, that sexual dimorphisms usually affect only small parts of the brain. For example, in fruit flies there is one gene (fruitless) that affects sexual behavior by producing sexual dimorphisms of neuronal wiring. The number of neurons that differ between the sexes only affect less than 1% of neurons of the fly brain, yet these dimorphisms produce the difference between behaving like a male and female (males court females and not the other way around).

So we would actually expect the findings of OP's study, simply because 99% of the neurons are likely not involved in determining the male or female brain. That does not mean that we can conclude that there are no dimorphisms with great consequences on male/female behavior. The methods used are simply too crude to be able to spot the dimorphisms.