Right, so the mother's nutritional status would have to affect something that affected sperm in such a way as to segregate the X's from the Y's. A change in cervical mucus consistency, making it harder for the sperm to swim? A change in pH that affects the more fragile Y's but not the hardier X's? Or is there something about the egg itself that makes it more "accepting" of X-carrying sperm?

Or we could be barking up the wrong tree and it could be about the environment that the embryo grows in that is somehow predisposed towards female embryos for some reason depending on the mother's nutrient status.

I just didn't find the mechanism the article put forth very plausible.