Anyone who watches any of the A.I. games can see that Chris Perkins is never really up on any of the official rules and always just seems to wing it. Even in this game he had to look up whether the enemies that had jumped on top of Binwin granted him cover or not. I suspect that he spends most of his time at WotC doing so much of the "creative writing" aspects of the game (monsters, story bibles etc.) that the actual current rules just fall by the wayside in his mind (until he's probably played them enough.) These playtest changes probably wreaked havoc on his memory of them.
So yeah... the players used the old critical hit rules that they remembered from their last game, and Chris either forgot what the new rules actually were, or just didn't care and let them roll max damage + an extra die. After all... these presentations have always been about showing the fun at the table in two hours, rather than a treatise on the "game" itself. Whatever kept the game flowing quickly and was the most fun is what Chris concerned himself with... not getting the rules 100% correct.
Personally, I've loved almost every single thing A.I. has ever done, and the Live Games at PAX have always been a highlight. I've found them to be a much more entertaining listening experience than many other "live game" videos or podcasts. I hope they always continue to do them.
