I think you are mixing up oats and oatmeal. And I think (but am not positive) that the study is referring to 300g of prepared oatmeal.
That wouldn't really make sense since amount of water could vary. Anyway the article says "Each oat meal comprised 100 × g of rolled oat flakes... boiled in water."
That wouldn't really make sense since amount of water could vary. Anyway the article says "Each oat meal comprised 100 × g of rolled oat flakes... boiled in water."