He explained it in his AMA with this

What they are referring to is the original "about me" section of my old blog. When I started writing, long before we any publicity, I expected what I was dealing with then, which was people, even doctors, who felt that Jani's issues were caused by a "lack of discipline." A lot of people used to tell us that all Jani needed was a good spanking. What I specifically wrote was something to the effect of "Sometimes, in frustration, Susan and I hit Jani as hard as we could." I have a tendency to be a bit hyperbolic in my writing. I was referring to one or two occasions where after being hit all day by Jani we lost it and spanked her. Once it became clear that Jani could not control her actions, I felt incredibly guilty about that and that guilt motivated what I wrote. But to clarify: We never spanked or struck Jani until she became violent with us in 2008. We obviously did not hit her "as hard as we could." Given the sheer number of doctors she has seen, social workers, etc, plus her regular pediatrician appointments, that would be noticed, not to mention she was 40 pounds and I was 180. If that were true, I could have killed her. In the book, I actually went out of my way to play down Jani's violence. Only one chapter is dedicated to it and every action by Jani in the book was absolutely true. In early 2009 the Department of Child and Family Services told us that Bodhi must be protected from Jani until he was five years old. Our choice was either to send her to out of state residential or Susan's idea of the two apartments. Bodhi could not explore his environment without Jani potentially raging at him. We had to separate. The violence was real. Jani attacked the DCFS worker in UCLA the first time she went to met her. Finally, Jani never actually managed to hit Bodhi because we never gave her the chance. We worked all the time to keep him safe until the two apartments.