What is going on with Shane's hop break can be summed up as follows: the CB is hopping (bouncing) backward in the air because the CB was in the air when it contacted the head ball of the rack (observed), and the reason the CB's back ward movement is arrested when it lands is because it still has some top spin (inferred).
Here is vid that shows the airborne CB:
With the vid paused, click on the timeline at 16:00 to advance the vid to the point at which Shane is down, getting ready to break. You may have to go short and click Play and then click Pause to land on that spot. This is easiest to do and easiest to see the break in full screen mode. He actually hits the CB at about 16:11.
Click on the gear icon near the lower right corner, click on Playback Speed and click on 0.25 (quarter speed) and click Play. If you leave your mouse pointer over the Play/Pause button and you are quick enough you can freeze the CB around the time it hits the head ball or just before.
If the CB was hitting head ball perfectly on its horizontal axis, on the cloth all the way, it would bounce backward but not leave the table surface. Because it is hitting above the horizontal axis it becomes a glancing blow. The physics of the resulting CB bounce is that the angle of incidence is equal to the angle of reflection, the same principle of an english-free ball rebounding off a rail, so the CB gains altitude as a result.
Although he does not stick the CB as well in this video the only way to get the CB to land and squat when hopping the CB is to have some topspin. You can prove this phenomenon by hand tossing a ball on the table. Unless you put back spin on the ball it will roll away from you after it lands. Because Shane's CB is flying backwards relative to the topspin it acts as back spin when it lands, working against the motion of the CB when it lands. Tennis players and golfers use this technique to control ball forward motion.
Why is the CB airborne when it hits? In this case he is breaking while resting his stick on the rail which puts his stick at a downward angle. So even if he hits the CB center ball he is hitting downward on it, causing it to bounce. In the case of this 7 ft table and video quality, it isn't obvious to me if he is hitting it hard enough that it does not touch the table again until after hitting the head ball or if it is bouncing along the way. While he does bridge on the cloth on 9 ft tables I have not studied video to see if he is still hitting downward on the CB but my guess would be that he is..
On the question of what he gains by the CB flying into the air, my take would be, not much. He has to hit the rack with extra force to make all this happen because force that could have gone into the scattering the balls was diverted into launching the CB. When I have watched his breaks over the course of many matches it seems he is relying on chance to pocket balls, the likelihood of which can be improved by additional collisions. This contrasts with someone that works on pocketing specific balls in the rack, such as Cory Deuel (and me), where using less force helps gain control of the breaking outcome.
One possible advantage is that having the CB in the air while balls are whizzing around the table might keep it from getting kicked
.
Because hitting downward on the CB when breaking will cause it to hop, the only way to avoid that is to get your cue as level as possible, which requires bridging on the cloth. In my experience it also requires elevating the bridging hand, what I call the stilt bridge, similar to bridging over an obstructing ball. While this bridge would appear to be less stable than resting the heel of your hand on the table it works well enough if you aren't trying to murder the rack.
When the cue is level and CB is hit just a little above center the maximum proportion of the force goes into the rack. The small amount of topspin causes the CB to arrest near center table after rebounding off the CB.
Assuming all of the balls weigh the same, the mass of the rack is 15 times greater than the mass of the CB, so not all of the CB force is ever dissipated into the rack because it resists moving long enough for the elasticity of the head ball and the CB to kick the CB backwards.
