Earlier quoted context omitted.
There is _no_ amount of butter (or fat, in general) that you can eat that will make you gain weight, provided there is no sugar in your diet. You will physically not be able to eat more than your body can deal with, this is because fat, unlike sugar, triggers the i-am-full hormones which make food impossible to eat.
No, that is plain wrong. Calories count, no matter where they are from. Ketogenic diets might increase your metabolism and reduce your appetite and hunger, which makes weight loss easier, but you'll still gain weight if you eat too many fat calories each day. Even if you cut out carbs entirely.
This is the exact point the article is proving wrong.