How many hours per day was he swimming?
Would it be possible for someone who was not supporting themselves that way? I.e. for someone with a 40 hr / week job?
My personal experience is that "outrunning" a poor diet is absolutely possible, and I kind of did it unintentionally. I started biking to work out of necessity. I wasn't planning to lose weight, but it happened. I had no weight loss ambitions or plans, but it was probably a good thing.
Shaq could easily dunk a basketball weighing 300lbs. You can't infer from that then that any person can weigh 300lbs and dunk a basketball.