His back foot comes up a split second before the snap. I've seen a lot worse go uncalled but he did move early.
I'm not sure it really does though. To me it looks like it comes up right as Jurgens starts to move the ball.
Now, you can make the argument that he wasn't reacting to the snap and just happened to move at the same time. But that's still legal. And there's basically no way the ref could be watching both places closely enough to tell the difference.