myth or rule?

[sc/nc ref]

I know I have read this situation on this site in the past, but I need some confirmation.
I saw it in the SC-Tenn game on Sunday, and had it happened in a HS game I was officiating tonight.
The ball is loose in the frontcourt. A1 while trying to retrieve it, slaps at it. His momentum carries him out of bounds on the endline. The ball stays in play. He then steps back in bounds, and is the first person to touch it. Is that a violation - or one of those myth plays that fans yell about but don't know the rule (ex - you can't retrieve your own shot, slapping the backboard is an automatic technical, ball is out of play when it hits the top of the backboard, etc.).
I thought I read on this site that it was a legal play. But the official in the SC-Tenn game (Pat Adams) called it a violation, and the college official I was with tonight called it a violation.
Note: In both situations, the player did not intentionally go out of bounds to avoid a defender (while dribbling stepping out to avoid a defender). His momentum simply carried him out, and he did not have control of the ball.
What is the correct call?
What if he did have control of the ball? (Dribbling, falls out of bounds, and comes back in). What would be the call in that situation?
Thanks for your help.