The gastric lining is usually divided into two regions, an anterior portion lined by fundic glands, and a posterior with pyloric glands. Cardiac glands are unique to mammals , and even then are absent in a number of species. The distributions of these glands vary between species, and do not always correspond with the same regions as in humans. Furthermore, in many non-human mammals, a portion of the stomach anterior to the cardiac glands is lined with epithelium essentially identical to that of the oesophagus. Ruminants , in particular, have a complex stomach, the first three chambers of which are all lined with oesophageal mucosa. 
I have to agree that the only valid point is the first one. The other points would be negligible at best and certainly not affect a high level natural bodybuilder. Body builders eat often but not such obscene amounts of food at a time that would make their stomachs protrude chronically. Heavy lifting also just doesn’t make your stomach stick out like these guys either. Maybe genetics could play a roll but I really doubt that too, particularly with the pros. Make no mistake at all, bodybuilders with stomachs like this are on or were HGH and/or insulin injections,.
A distended stomach is a term usually used to refer to distension or swelling of the abdomen and not of the stomach itself. When the term is used in this manner, a number of different diseases and conditions can cause abdominal distension. These conditions can be related to digestion , such as malabsorption or lactose intolerance , or to disturbances in bowel function, such as irritable bowel syndrome ( IBS ) or constipation . Bloating is another term that is sometimes used to refer to a swollen belly. Consumption of high-fiber foods can lead to intestinal gas and bloating. Less commonly, ovarian cysts or other types of tumors can cause the appearance of a distended abdomen . The accumulation of fluid in the abdominal cavity, known as ascites , can cause the appearance of distension. Ascites has a number of causes, including cirrhosis of the liver .