Are you serious right now? She didn’t deck her bf randomly. She was assaulted and her bf made the poor decision of sneaking up on her. 
In this scenario, the sexes ARE NOT reversed, so there is zero need to be doing the blame game about how if she was a guy and he a girl, people would be up in arms. Take the scenario for what it is and stop blaming this poor girl. 

OP, I am so happy you are seeking out help. I am happy your bf was understanding, he needs to be much more aware of his actions, but you also need to be aware of yours too. This was an accident, and once is OK in my eyes given the situation and how you then handled it.