Hi Yowie,
i know the exact feeling you are going through but I wouldn’t stress about this.
You weren't arrested or charged, and you have a clean record therefore you would tick "no".
My partner has a record, which was my concern. After looking at multiple websites for relief we decided it'd be best to book an appointment with the U.S consulate and see whether or not he would need a Visa (mind you he was approved the Visa Waiver straight away)
We paid $180 to get a copy of his record, which outlined his charge (Affray T1), He met with the U.S consulate in Canberra and discussed his arrest and whether or not he would need to apply for a Visa. He was told as his Visa Waiver was accepted he doesn’t need a Visa and Affray T1 doesn’t fall under Moral Turpitude.
I couldn’t tell you exactly what went on in the meeting as I didn't go in with my partner, what I do know is he is elligable to travel under the visa waiver program. No matter what you have though (Visa, or Visa Waiver) only the customs officer at the port of entry has the final say whether or not you get in.
I did speak with others about this, I was surprised to hear the stories, for instance a friend of a friend had previously assaulted a police officer, had multiple drug charges however ticked "no" on the ESTA and got in , no questions asked.
I hope this helps in some way, but if you are like me, you might want the opinion of those that know best - the U.S consulate.