I know how he does this, he does a really difficult “card mechanic” move where he braces the cards that are face up differently in the final “shuffle” against his fingers in a certain way, and braces all the face down cards in a different way against different fingers perhaps. The 2 cards penn and teller chose are also braced the way they need to be, so they will be the only cards face down. Then he sort of does a wave of his hand while also pulling the two stacks apart, and putting them back together, a cut if you will, but all the cards he pulls away are either face up or face down, and the ones left are opposite. He then turns the cut half so they all match, except the 2 penn and teller picked.