About movement 16 and the American judge giving a 6, that movement says transition from collected walk to piaffe, not from piaffe to passage. It’s for transition into piaffe, not out of piaffe. I agree there was no transition out of piaffe, unless piaffe to back/rear/spook is a movement. 
But that movement was transition into piaffe. Clearly there is a difference of opinion in the judges on whether Satchmo entered piaffe fine (movement 16) and then spooked, resisted once in piaffe, or whether he never actually established piaffe before spooking/resisting.
I’m not casting a vote either way, but I could see both interpretations watching it, so I don’t think the American judge’s score of 6 is from left field. From the scores, he apparently thought the horse was already in piaffe before resisting and entered piaffe reasonably well (6). Two judges thought he did not establish piaffe well at all but did establish it sorta (2 and 3). Two judges thought he never established the transition into piaffe before the freakout (0).
Edited to add: Sorry, found another listing of the movements. I was relying on the info above post 184 that said transition from collected walk to piaffe was 16. It is transitions both into and out of, apparently. Does leave a question mark on the 6.
