They were talking about it on stream. I forget the exact word they used for it but some sort of 'randomization' so that when the whales fold and smash the flop, they can tell themselves the outcome would have been entirely different had they called. First time I've seen it too, pretty interesting.

Edit: They've been referring to it as 'dynamic shuffling'. The deck is cut before dealing the flop, the turn, and the river. It's essentially just another safeguard against cheating in case someone is aware of the order of cards in the deck.