I know it's only one play but the more I study that particular play the more I'm convinced Schaub is a one-read QB. There were only three receivers out on that route, the rest stayed to block giving him max protect upfront. And yet he totally ignored Walter when he realized AJ was covered underneath and opted to throw to the one guy that shouldn't be thrown to unless he was under great duress in the pocket.
http://imageshack.us/a/img99/1356/schaubint.png
The way it's supposed to work, is that Schaub already knows where his guys are going. What he doesn't know, is where the defenders are going. So what they generally do is key off a guy or two on the defense.
It looks like Walter is about to break to the outside, but for all we know he's trying to get that safety to move outside so he can cut back in. So
maybe (& I don't know any more than you do so I'm saying maybe) Schaub is watching that safety & since he knows that safety isn't moving, KDub is already out of the equation. Not only is there a safety on top, but a LB underneath. That would be a difficult throw, over the LB in front of the safety.
When you break down our defenses, try to find an instance when our LBs get that deep & stay shaded that close towards the receiver. (there are times when getting that deep isn't required, down & distance & the route combination should be your guide). He's got his eyes on the QB, but he sees (or "feels") Walter out of the corner of his eye.
That guy playing on top of Andre is not the guy Schaub should be looking at. Instead, it's that LB between Schaub & Andre. If Andre is to turn out, towards the sideline, he's open. If he turns inside (which it looks like he is) then he's not. Being that Andre is a gifted athlete, it's possible to throw the ball high & give him a chance to make a play. But that LB is so deep, even that would be a difficult throw (if Andrew was to break inside).
The picture you have doesn't really show it, but if you look at the motion of the defenders, they're already moving in the direction of the throw. Meaning the already know where he's going with the ball. Most likely because he patted the ball, or he reset his feet in that direction (which is what makes a 3, 5, 7 step drop so effective, your feet are trained to point where your eyes are looking when your last step drops & defenses don't have time to react). But that's why the ball was intercepted, he was late on the throw. He had somehow or another signaled where he was going & allowed the defense to react before the ball left his hand.