RRoP:
"1. Your hand is declared dead if:

(a) You fold or announce that you are folding when facing a bet or a raise.

(b) You throw your hand away in a forward motion causing another player to act behind you (even if not facing a bet)."

This is 100% an insta-fold. Irrevocable. Doesn't matter if cards are retrievable or not.
Unlike at showdown, you don't get to change your mind facing a bet.
Forward motion and releasing your cards facedown while facing a bet is (or should be) universally a fold.
Not the same as forward motion with chips, which may or may not be a bet, depending on local rules.
Bad decision by floor.
Several other recent threads on this in B+M, BTW.