I've thought about this a lot since seeing the video and am guessing that he probably has diastasis recti, a separation of the two groups of abdominal wall muscles. This condition is ordinarily seen in women as a complication of pregnancy, but can occasionally be seen in men as well, generally as a result of visceral fat related to severe obesity.
Here is a man before and after developing a mild case of diastasis recti - note that his stomach is also slightly bifurcated vertically right in the middle:
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Of course, Ethan has so much subcutaneous fat that he also has a massive wall of flesh hanging down from his stomach, which combined with the visceral fat-induced muscular separation would lead to an unusual distribution of fat, potentially causing a bifurcated gunt of the sort seen in the video. To get a gunt like this one, you'd need to have both a large amount of visceral fat and a large amount of subcutaneous fat, which doesn't happen for everybody even if they're severely obese.
This analysis is speculative but it's the best explanation I can come up with and is definitely not in any way medical advice.