Earlier quoted context omitted.
The idea that eating fat leads to higher body fat is the most dangerously-wrong health misconception in history.
Honest question: how? I've never seen anyone who's obese and having a diet that made me go "huh that's odd how can they be obese?" While the inverse occasionally has been true, generally people who I consider in good shape appear to eat less, and less greasy food. So while there might be exceptions it seems to be a damn good rule of thumb to me.
Your question isn't refuting OPs claim: the people you are observing to be fat are fat because of their carb/sugar intake, not fat.
i.e. if you just fed someone large amounts of protein and fat they would be lean; it is the sugar and carbs that make them fat.