By rule, he is not airborne. His hand is on the ground, in bounds, meaning he is not airborne. Therefore the advancement of the ball, even if it is out of bounds, continues until he lands out of bounds, or his hand lifts at which time he is airborne.
I saw a good explanation of this ... let's say while tight-roping down the sideline the WR held the ball out over the sideline, and the ball was actually out of bounds. So, you have a runner in bounds running 20 yards, as an example, and he has the ball held out over the out of bounds line. After running 20 yards he steps out of bounds. They don't move the ball back 20 yards to when he first held the ball out over the sideline. Same here ... so long as Bowers has his hand on the ground in-bounds, he is not airborne, and the ball being out of bounds can keep moving forward until it hits the ground, any part of him hits the ground, or he lifts his hand off the ground.
So, the problem with your position, IMO, is that you aren't defining "airborne" correctly.
Another example is a WR who keeps one foot in bounds as he leans out of bounds to catch a ball. As he is falling down, with no body part out of bounds, and at least one foot on the ground, he can hold the ball forward as he falls and when he hits the ground the ball is marked where he was holding it, not where it crossed the sideline before he caught it.