I cannot see what the fuss is about. She was under an obligation to put the allegations in context, for people who had not been aware of the situation. This was presented as an example, of the abuse Johnson’s former wife suffered. She did not say it was a one off - those were comments from Johnson’s cronies.
Bruce could not have said ”Well, yes but it was probably a string of attacks over many years”, because she had no knowledge or information or evidence that was the case. She was stating a simple FACT Johnson’s biographer stated an instance of abuse, and his friends trivialised it. And after all “They would say that, wouldn’t they”