Hmmm, perhaps you meant the (very real) threat of informing the captain who could ban him from the flight is what worked. Unless there is current (not latent) and undeniable proof that the GA was absurdly out of line, I expect all UA employees to have each others backs, especially those with the ability to deny service like a captain. Clearly, the interaction/altercation was not worthy of changing or delaying travel plans, as it shouldn't be.

Some people are more easily provoked than others and each of us has our weak spots or breaking points, both as passengers and airline employees. Those points vary day by day. Never know when something simple will get out of hand, and it is best to back down (be the bigger person) yourself, regardless of your legal rights. If your legal rights are violated to an extent where damages are due, the court system is set up to handle that after the fact, and UA has the ability to play ball with you in that system.