Two things. First: The rules. They state since a couple of years: Yellow in the penalty box, if it's a foul but the defenders challenge was for the ball. If he holds, pushes or pulls: It's still red, if he denies a clear goal scoring opportunity.

Second: The ref obviously punished the holding. So therefore red is right. But I also agree that that was a very soft penalty because that was not a real holding and the defender did challenge for the ball and even played it.