It's not just the yeast but there are dextrins in your beer.
A dextrin by any other name is simply a complex carbohydrate produced in your grains. Mashing, decoction and the boil process will influence your dextrin content, too. Less highly modified malts and the kilned dark crystal are fairly rich to begin with so when you're doing a "big beer" with a higher specific gravity, expect some leftover complex carbs, expanding CO2, and yeast aftereffects from digestion.
Modifying your recipes and process can reduce your gas issues but it's something all beer lovers should expect. Your inherited traits from your relatives affect your digestion, too, Some people have issues with lactose and others are sensitive to breads and vegetables like beans, peas, lentils, zucchini, and squashes. When you drink a beer with this sort of food the gas effect will be magnified.