I can understand the Director being upset with them and giving them a hard time about their performance, but the cursing is unprofessional.
Now high school football coach, I have heard that type of language, but those guys did not seem phased.
Before you EVER go above the head of a teacher/ instructor, you always speak with them yourself. That is the first thing the Principal will ask you. "Did you speak with the Band Instructor and what did he say." Remember if you are working and someone has a problem with you, you would want them to speak with you directly, before they went to the President of the company to complain about you.
So if you feel strongly about this, think of a non confrontational way to say "Hey, I was passing by and heard you speaking with the section of the band. I could tell you were really frustrated, but I was surprised you cursed at them. I feel like they look up to you and want to please you by doing their best, but the cursing was not needed to get your disappointment, expectations and direction to them. "
And mom, it does not matter if you felt the band played great, the Director knows how it is to be played. Parents usually do not notice the mistakes.. I know our daughter is always perfect.. Hee, hee.