"VIOLENCE? Tapping someone with a newspaper is now violence? "
Only when a woman does it to a man. A man hitting a woman really hard OTOH, is not violence.
"What the guy did was wrong, what the OP did was wrong. " What the OP did, was nowhere near as wrong as what the guy did. She did not actively try to hurt him. He very probably did actively try to hurt her.
"To be honest my son hit me on the arm when he was 3 and it really hurt"
Did you smash his face in to teach him a lesson and show that he can't get away with hurting someone without being hurt himself? Or are you sane? 
Why are people equating "playful office banter" that went too far for one person's liking with domestic violence?
Because it's exactly the attitudes on this thread - bending over backwards to excuse this man's violence, picking apart the OP's behaviour (which was not good, but that is not actually the issue here), demanding that a female victim of male violence is perfect and behaves well and correctly at all times otherwise she brought his violence on herself, which enables men to get away with beating up 1 in 4 women on a regular basis. Domestic violence is not a separate thing, done by different men to everyone else, cut off from the rest of the world with different women. It's an intrinsic part of society and the reason it is so common, is because we enable men to do it.
The attitudes that make excuses for men who batter women at home, are here, on this thread.
That's why people are making the connection.
It's not difficult if you bother to think about it honestly.
The two situations are not comparable and I think to equate the two is downright bloody insulting to anyone who has suffered