I had a similar experience recently: Facebook and commenting on the show. Granted, this was not involving an orchestra, but it involved one of our rail guys against my stage management team.
We were in tech, and while a extremely heavy wall was coming in, the chain motor broke, which caused the chain in it to come loudly crashing to the deck. The wall stopped in it's place, but all anyone who was backstage could do was listen to the horrific noise, not know where it was coming from - and run. Since we had no idea where the noise was coming from (and we didn't know it was the chain motor that failed) we worked to get out of the backstage area. Once we could see the chain start to pile on the deck, we stopped running.
Now, not one of my better choices in life, as we all make mistakes, I commented on facebook during dinner that "I learned something today: 200 feet of chain is extremely loud when it falls from the grid and you really can't tell where it's coming from." I did not lay blame on anyone, I didn't say anyone got hurt, I didn't say where I was or what show I was doing. However, in retrospect, I shouldn't have posted about something dangerous happening at work. Word got around during the half hour call that I had posted, what I felt, was a harmless statement. The house Head Carpenter was upset and confronted me about my post. He had only heard of the post from another crew member, since he was not on facebook. We discussed it, and I agreed to take the post off of my wall. In the end, both he and I came away from the situation having come to a mutual understanding and were back to our usual friendly relationship.
Later that night, our Master Electrician told me about a rather rude and insulting facebook post our railman for that show had made. I could not see the post, since I was not friends with the railman, but I was told that it was really mean and rude towards me and my entire stage management team. She then told me of others who had commented on the post, agreeing with the railman. I felt I had probably started the problem by commenting on the chain, but I thought it would go away since I had taken my post down. The ME went to the railman and told him I had taken the post down, but he did not care. I did my best to ignore the situation and remain positive.
The next day a complaint was lodged against me with the local head of IATSE (the stagehand union). The complaint was that I said a very specific profane phrase during tech and that the crew should not be subject to such language. The IA head contacted my Technical Director who then called me just before tech the next morning and said I should not curse on headset. I was literally blown away - I knew that I had not cursed (and definitely not the specific phrase in the complaint) during the entire tech process. I may have said the "S word" when one of my principal men almost dropped my star ballerina the night before, but I remember saying it very low and that my headset may not have even been live at the time.
I went to my ASM and PA, along with the Master Electrician (all close friends of mine), and asked them to rack their brains to try to remember if I said that phrase, or if I had even cursed at all the night before. They were all at a loss. The ME and I went through the entire crew list thinking of who could've made the complaint, crossing off the members of the crew that were regular cursers, as that would be a case of the "glass house" that you mentioned happening below. We ended up with one person: the railman that made the negative facebook post. I told my TD that we were all certain that we had not said that phrase, and I really hadn't cursed at all (though I had in previous years when major catastrophes had happened - oddly enough all had involved the rail...) during this tech process. I then brought up the negative facebook post from the railman, and I told him of my own post which may have provoked him, but that I took it down.
My TD went back to the IA head with this information. The railman was reprimanded for writing on facebook horrible things against my SM team and the company I work for, it was revealed that the profane phrase was actually from a show that took place 2.5 years ago (which I admitted to - it was a horrible rail/supernumerary screw up that was obvious to the audience) and the railman was then removed from all future productions that my company will ever perform.
Hindsight: never post anything negative about your show on social media.
Granted, in your situation it sounds as if you did not post anything to start the ball rolling, but you have seen how these things get out of control and people's feelings get hurt. There's the "6 block rule" - but that can't hold water in social media. The best thing you can do is ignore the post, and recommend to your crew that they don't fuel the fire of the orchestra by commenting back and forth on the topic. In my situation, there were managers over each area, and complaints about the other party were lodged with those managers. If you were acting as the SM for your show, perhaps you could've gone to your TD (if they are school staff) or Department Head and let them know what happened - your crew person made a mistake and the orchestra is upset, but now it has escalated into an uncomfortable situation. Hopefully your TD or Department Head could talk to the Pit Director, and from there the Pit Director could talk to the orchestra about professional show courtesies. You're experiencing this in high school, and I'm experiencing the same thing 10 years into my professional career. Take this opportunity to learn this lesson now, instead of being like me and learning it far too late into your career.