The bunt call depends on if the bat hit the ball or if the ball hit the bat.
NFHS isn't particularly clear in the rule book, but it is covered in the umpire case book. (page 48) If the batter hits the ball in fair territory and lays the bat down and then the ball subsequently hits the stationary bat, it is a live ball. Said live ball could then roll foul making it a foul ball. However, if the batter drops the bat and the bat while still moving contacts the ball in fair territiry, the ball is dead and the batter is out.
NSA Rule 7, section 6 covers this situation.
Sec. 6 The batter shall not hit a fair ball a second time with the bat in fair territory.
EFFECT: The ball is dead, the batter is out and baserunners may not advance.
EXCEPTION: If the batter is standing in the batter?s box and contact is made while the bat is in the batter?s hands, it is a foul ball even if the ball is hit a second time over fair territory.
NOTE: If the batter drops the bat and the ball rolls against the bat in fair territory and, in the umpire's judgement, there was no intention to interfere with the course of the ball, the batter is not out and the ball is alive and in play.
I don't have the ASA rules, but I suspect it is the same. No doubt Bretman can expand on all this, but my feeling is it was quite possible you got the correct call.