Men with higher testosterone levels are more likely to produce male offspring. So I agree with you. It seems easier to put the gender bias mechanism in the males.
In particular, the statement "men who have higher testosterone levels are more likely to produce male offspring" is pretty much equivalent to the statement "women having sex with men who have higher testosterone levels are more likely to produce male offspring", unless it was measured by impregnating women in a double-blind setting. If it was based on conceptions from a sperm bank, it might be better evidence, though my understanding is they still generally report some information to the women about potential fathers and give her some choice in the matter (but I could easily be mistaken, there).