I guess it's possible that he had way too much yeast and a combination of a carb-rich diet, poor digestion and a buildup of starch in the colon could result in the production of a decent amount of alcohol. Your colon has a lot of blood vessels so it's very easy to get wasted from alcohol in there. Google wine enema.
Still, the story seems like a stretch. If this guy was a homebrewer then he definitely should have figured this one out, especially after he turned his butthole into an airlock.