Of course there is some flex. But contrast it with a retraction turn where the hips moves more on a level plane. In this case the hip and upper body makes a distinct up and over move. The difference seems obvious. This is not the "perfect turn" but we see it often and in top level skiing. I'm wondering why.
Inexact Harb quote- "1 mm of flexing at transition is in the right direction, 1mm of extending is in the wrong direction."
What to look for is as Soft Snow Guy said- look at the outside knee. But also look to see if the outside knee flexes before the inside leg extends.
*if you aren't interested in skiing the PMTS way, just ignore this post.