Perhaps he was a bit over the top, but the point is right.
I know, spanking threads, blah blah blah, but I have yet to see anybody give a rational justification for violence against a child. And yes, if the intention of the punishment is to cause pain to the child as a means of deterrent, then it's violence. If someone disagrees I would also like to see the reasoning behind that conclusion.
All you have to consider is if you did this same thing against an adult, would it be considered assault/battery? If yes, you probably shouldn't do it. There are better methods of discipline than beating children.
Also, "It happened to me and I turned out fine" and "Well, it worked" are not valid arguments in this situation. Efficacy is not a measure of morality.