You're somewhat delusional if you believe this was pure fat loss. I regard it as a disservice to give people the impression that this kind of fat loss is either possible or healthy.
At the level of exercise required to sustain a caloric balance of -2700 calories per day over four months, the body would become severely protein challenged. Even converting fat to energy increases protein demand, as those organelles burn hard and wear out.
What happens with formerly fit individuals who then become obese is that these individuals actually have extremely large reserves of skeletal muscle (obese people tend to have extremely strong legs for practical reasons, it just doesn't seem like it as hefting their own body weight consumes most of their strength). As this kind of person goes into an endurance exercise program, he or she actually needs far less muscle mass than they have starting out.
If his story is true, I bet he lost a great deal of skeletal muscle mass in addition to a lot of fat. The muscle that remained would be extremely fit and efficient, but less strong.
A similarly obese person without the muscular reserve would be flirting with death in attempting to replicate these figures. If his story is even true. And if it is true, why did he quit and put all those pounds back on again? Could it be that his body figured out that the stress of the program was unreasonable to begin with?
Did he actually measure his body composition before and after, or did he just take a weight difference and presume that anyone who exercises that much couldn't possibly have shed any muscle mass?
I don't feel like digging up particulars I last read five years ago, but I distinctly do not recall having ever read anything credible which suggests this level of weight loss can be achieved on a pure fat-burning basis.