You said that the swelling of the cat's stomach may be due to intestinal inflammation and edema, and intestinal bleeding can cause melena. If possible, take the cat to the hospital as soon as possible. The most accurate routine examination in the hospital is that cats will get infectious peritonitis (because abdominal transmission will be accompanied by symptoms of dyspnea).

If it's just intestinal bleeding, give the cat anti-inflammatory drugs, depending on the cat's age and weight.

Although I don't know what cats eat, in short, feeding stray cats instead of human food will hurt them.