First thing Full Disclosure: I am an Authorized Stack & Tilt Instructor.
The pictures in Golf Digest of Aaron Baddeley were a DRILL that Aaron was doing to correct him staying in flexion in the backswing (moving upper centers to the right). There were supposed to be three photos: a before, the drill or his feel (which was pictured) and then the after. BUT many times Golf Digest or any other magazine does not print it in the exact way you want. In that picture of Aaron, if you reread the article just below the picture it says ....some players MAY HAVE TO FEEL as Aaron is demonstrating.
Now as for a reverse pivot...the definition you stated is wrong. You can have a left anchored pivot if your weight started left, stayed left and moved left. That is not a reverse pivot. If your weight started 50/50 and moved 90L & 10R on backswing, then moved 90R & 10L on downswing to finish then that would be a reverse pivot.
Stack & Tilt teaches a centered pivot. In all teaching, to change someone you many times have to go to opposite feels. It just as easily could be someone with a bbig hip slide to the right and a huge reverse spine angle....in this case you may have the player feel like his hips stay left and his upper torso moves to the right. So you could overhear me given a lesson and make assumptions about what I teach which has no basis of fact...as my lesson was about fixing the guy I was with and HIS issues.