The motion path is Referred to by the DWPS or the UWPS. this tells the reader whether or not the pick escapes on the Upstroke or the Doenstroke. The grip/Arm Position, and the mechanic used is disclosed by whether you are Pronated or Supinated.
Pronated Deviation is a UWPS movement.
Supinated Deviation is a DWPS movement.
Mechanically these two are the same motion- they’re both Deviation. It’s the arm positioning that changes the slant of the trajectory.
Promoted Extension/Flexion is a DWPS movement.
Supinated Extension/Flexion is an UWPS movement.
There is only one wrist movement to create one of those 2 slanted trajectories when Pronated or Supinated.
If I say someone is doing Supinated DWPS then I know that immediately that they have to be using wrist deviation as from that arm position and grip of being Supinated and the trajectory path of DWPS that the wrist deviation is the only mechanic that provides that path.
In Andy’s case. His pick has a “Downward slant” but yet he is doing an UWPS motion. This is Supinated UWPS. This tells me that he is in a Supinated position (causing the visible downward slant of the pick) but using Extension/Flexion to create this motion path (the Reverse Dart Thrower motion) to create the UWPS trajectory instead of pure wrist deviation which would create a DWPS path.