what to call? could not find in rulebook!

[Bandit]

Wow, lots of questions could come with this one..I dodn't know why the runner decided to go back but if the BR was already called out and the runner retreated to first base and arrived before anyone tagged him, he/she should be safe...Why did the umpire call an out??? Can't look for a dead ball, baseball or fast pitch softball, the ball would still be live. I think I would have a out for the BR, and dumb runner still on first.