Did this study account for lane positioning? The distance at which I get passed corresponds directly to whether I take up more of the lane (good passes) or ride far to the right (close passes). If this factor wasn't accounted, perhaps women are getting passed closely more often because they ride too far to the right more often thinking they'll put themselves in less danger. We already know women take fewer risks than men (
http://journal.sjdm.org/jdm06016.pdf), and it is often instinctual to ride far to the right thinking it's less risky.