That wouldn't work if Toph actually can't sense mid-air attacks. Roots grow in tall trees, yes, but they're still connected to the ground. This guy, on the other hand, leaps into the air with no connection to the ground below whatsoever, and launches attacks at her. Either Toph is so intelligent that she calculated exactly how long he would be airborne, what angles the attacks were coming toward her, exactly where he'd be in the air (since he'd likely start descending around this time) to redirect the attacks back toward him, or she can sense attacks in mid-air.