Once his belly reached the point of no return... his fate was sealed. 
That's what HGH does to you. Compare the round shape of his head vs the HGH head that developed over time.
GH contributes to it but maybe not for the reason you think. It's not internal organ size so much, if it contributes to say heart failure then yes, the stomach fills up with water. Even without heart failure GH increases general water retention. What you see on his skull is volumized muscle, not bone growth, and GH does that. Same reason hands and feet seem to grow on GH, it's not bone growth but water in the muscles and other soft tissue. The muscle between the thumb and forefinger swells up. One effect GH has is the tissue under the chin swells up and it may look like a regular double chin. These effects are temporary while you're on it. Even Duchaine decades ago remarked that the positive effects from GH seem to disappear within days after stopping; it's because it's water in the muscle.
I've had water buildup in the stomach cavity from CHF and recently also from pancreatitis inflammation so I can tell what water there looks like. Another possibility could be ascites from liver failure.
