It's impossible for anyone here to say why the call was what it was. It apparently may not have been right, based on the info we have been given, but we really can't know what the umpires were thinking or why they ruled the way that they did.
Are you sure there weren't any outs to start with?
What coach worth his salt allows an extra "phantom" out to be charged to his team without talking to the umpires to see what's going on? Nobody piped up? No scorekeeper, no assistant coaches, no players, no fans? No one was screaming about there being only two outs?
Frankly, that seems way less likely than "there was really one out to start with".
I was keeping score with Iscore app. Sort a missed it all when the the interference call was made. The umpire asked the coach to get out of his face so no one asked for the scorebook when all this thing was going on. Everyone was pumped up. The coach was telling the umpire about 2 outs but he would not listen to her. This is her first time coaching high school ball too. So when I score showed next batter of our team, i though I may have messed up and just a gave that batter an out and finished the innings.