Batter Interference NFHS

[BSBAL18]

IN the case book, quote
"With R1 on third, R2 on first an no outs, R2 attempts to steal 2nd base. The pitch is strike 3 on the batter, however during F2 attempt to throw out R2, the batter interferes and the ball sails into the outfield, resulting in R1 scoring from third. RULING: The batter is out, and R1 returns to third base because that is the base he occupied at the time of the interference. IF the umpires judgement believes R2 would have been out on the steal, then R2 is out, otherwise R2 returns to first base".

So my question is...
I have always seen batter interference as the umpire calling dead-ball and calling the runner for 1st to 2nd out. Is batters interference differnet depending on the number of runners and "if" they are stealing? The case tells me that if I, the umpire, think they are going to throw out Ricky Henderson, then he's out, otherwise return to first. Perhaps MLB rules are different that NFHS in this regard?
What if there was a double steal? Why does R1 have to go back to third, but R2 is "umpire descretion".. i have no idea if its a delayed steal from 3rd, etc. How can i call a runner out if i dont even know if the defense had planned to throw the ball directly back to the pitcher to try to pick off 3rd base???