He was growling, barking, hackles raised, and running away from him. We tried to soothe , pet, and reassure that all was okay but nothing worked.
From what I've read, when your dog is scared, do NOT reassure, pet, or soothe. The idea is that by doing so, you are reinforcing the behavior and fear. Your dog doesn't understand English, so he thinks he is reacting appropriately because you are, in a sense, rewarding and praising him while he is acting out of fear. In other words, by saying, "Good boy!" you are saying, "Good growl, bark, and fear!"
Instead, say nothing. Give him calming signals. When he shows calm or "brave" behavior, THEN you treat. And, when he is scared, work on taking deep breaths yourself . . .think happy, calming, everything-is-cool- thoughts.
But like others said, maybe he had an instinct about the guy . . .