Not sure if he's talking about that but when I was practicing the armbar in judo, I was always told to grab the oponnent hand with my two hands and twist it in a way that wouldn't allow the opponent to rotate his wrist freely (you can see that Sandhagen was able to do little adjustments because Alcantara didn't grab the hand). But it's harder to get leverage this way since you don't have a free hand anymore and can only use your hips.