Thanks for your excellent explanation of this. By the way, have you noticed that right at the end of the trick Derren thanks the guy and says "that was Out of this World" - typical Derren mischief and giving a nod and wink to those in the know.
Best wishes
Mark

Our reply: Thank your for your email! Yes, we noticed that - in fact, it is our favourite part of the trick. We hope you are well!