Did I say that? I think I carefully inserted the word "relative". Let's take the case of straight down the fall line turns. Ideally, the skis/feet are going to be flat as they pass underneath the body and the hips are going to be travelling at a constant speed down the fall line. The hips must moving to the inside of the new turn through the transition. Either that or you'll need to take my crack pipe and my chocolate Easter eggs away.
Yet, with respect to relativity, I also agree with the "ok for them to move back" comment. My perspective is that as the feet pass under the body, the hips can be moving back relative to the feet but still be relatively moving forward into the new turn because of the path of the feet. This is Bob Barnes' argument against forward movement in the turn. My opinion is that this is a classic example of two people saying "black" vs "white" yet meaning the same thing. I'm ok with whatever definition works for my students, but I've never had to deal with this kind of semantics on snow because the focus on cross under turns is feet not the hips.