If it's true, he might just not want to get his bell rung in sparring; so he can stave off possible pugilistic dementia in later life. A lot of guys in mma and football are looking for ways to lower the amount of concussions they receive in training too. Though the account does sound suspect.
Reminds me of the time i got thrown out of the Klitschko camp for knocking Wladimir out of the ring with a 6 uppercut combination.
I knocked the **** out of Wlad when I started whistling the Star Spangled Banner. He cut at the first sharp and fell unconscious at the first flat. I had to sign a non-disclosure in order to leave the building and avoid getting iced by the Kiev mob.