Dogs behavior is very complex, as it is based on pack mentality from wolves. Your dog is likely to try and protect you, it sees itself as head of the pack (this is where trainign comes in, to show that your are head of the pack, and don't need protecting).
Aso dogs tend to be inquisitive, social, and act in self defense. One will go over to another and very quickly a fight can break out and the blame can't really be attributed.
Violence towards animals solves nothing, it might even provoke them. your dog in this example may have a particular dislike for this man now, and will probably growl at him- understandable really. But doesnt help your situation if you meet him again.
Be confident, and keep your dog on a lead wherever possible. We have had problems with people acusing our dog of being agressive, when shes just been to freindly, annoyed the other dog and so on.