I agree he uses a mem deck. Years ago I started learning the Aronson stack after reading some books by Michael Close. I didn't stick with it so the stack didn't stick with me. But Simon Aronson and Michael Close have some really astonishing effects using this technique (such as a gaff-free Invisible Deck).
As to really memorizing a shuffled deck, this is a standard phase of formal memory competitions. I believe the world record for correctly memorizing a randomly shuffled deck is just over 15 seconds. Astonishing indeed!
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