The difference is I just used your example to show you that someone in the end zone touching the ball establishes the ball in the end zone. The punt returner, standing in the end zone, touching the ball, automatically establishes the ball in the end zone. You asked about the gunner jumping and then batting the ball out of the end zone. Ask yourself, why did the gunner jump (from outside of the end zone)? Answer: because if he establishes himself in the end zone and touches the ball, it's a touchback. I'm not getting anything confused. Guess what, if the punt team touches the ball in the end zone, it's not an automatic touchback. Someone on the return team could pick it up and run with it. The end zone works a lot like out of bounds, if a fumble touches a player who's foot is out of bounds, the ball is out of bounds whether it actually goes out or not.
Fact: The punter kicked the ball into the end zone. The only way for another player to change that is to touch the ball while that player is established outside of the end zone. The returner was standing in the end zone, therefore established in the end zone, thus the ball was considered kicked into the end zone as soon as the returner touched it. I have explained why you haven't seen a punt returner field a punt in the end zone earlier. Basically, unless the coverage is over kicked by about 40 yards, there is nothing to gain.