Your actions were not over the top. Nothing wrong with a small friendly tap when someone is not moving. On the other hand, a person who reacts like the father did and accuses you of "shoving his son" is an idiot--plain and simple. A tap is not a shove. He has serious issues and just wanted to fight.
I agree, a lot of people touch others to get their attention. The Father was the one with the over the top reaction.