He picked up one of the better offensive players in the league at 40 feet. Denied the 3PT attempt and stayed with Young to the hoop to contest the shot. Stewart rotating is how defense is done, he is supposed to be there for the contest to take away the middle. That is why Ivey is fading Young to his left, so there is only one angle to the hoop and it gives Stewart a shot to block it. Even without Stewart, Ivey is there to contest what would be a hard shot to make. That is all you can ask for when guarding someone as talented as Young.
If we want to nitpick, we should talk about Cade. Ideally you want him to slide down inside of Okongwu to replace Stewart. But whatever, he got the block to recover.