Pushing someone does not equal assault.Jonny has admitted to physically abusing her, she was blocking him from leaving a room and he said that he pushed her out of the way so he could leave the room. Under the law this is physical abuse. His only two options were, go sit back down or call the police. he did not have the legal right to touch her without her consent. Only if she had a gun or knife pointing at him or attacking him then he would have been legally allowed to defend himself.
The jury will make that decision anyway. And I can guarantee that they won't classify it as assault.