Batter intereference with catcher's throw

[Ran.D]

Wearing my coach's hat last weekend, and a call has been bugging me.

16U Fast pitch, One out - runner on first.

Batter strikes out and heads for 1B dugout, runner steals on strike three and is safe. Fans/parents allowed to sit directly behind plate complain that batter got in the way of the throw and complain.

BU & PU confer and Call - stealing runner is out, end of inning

Courteously, I ask for an explanation and was told that the batter "waved the bat enroute to the dugout".

I have never seen this called before unless there is contact between the batter and catcher, batter and thrown ball, or an obvious attempt to get in the way of the throw.

Appeared to me the catcher got the throw off cleanly and the runner immediately headed for the dugout.

Shouldn't the PU immediately call dead ball, if he SAW interference, instead of waiting for the result of the play?