I'm responding since I also saw the Crushing Hammer played after the Unfair Stamp. There was no cheating however, if what Natalie said the translator said is true, then Hiromu Sasaki lied to a judge which is a disqualifiable offence but it could have been a translation error.
I played against Hiromu Sasaki in round 6 of Melbourne Regionals. In game 3 he played Unfair Stamp, drew 6, played Crushing Hammer, flipped tails, realised he drew 6 and pointed it out. He took the Crushing Hammer back and I called a judge.