I myself am doing keto with Ketochow (a Keto-esq Soylent mixture made by a gentleman out of Utag), and lose 3-5 lbs a week on it (yet it tastes like delicious pancake batter) while doing minimal exercise.
It's obviously a combination of eating less and losing water weight. Your body can maintain about 1 lb of glycogen and 3 lb of water associated with that glycogen. Not eating carbs will likely lead to a big decrease in this weight. Also the fat itself is stored in 1:1 ratio with water. So your 3-5 lbs per week is likely either a 1 or 2 time thing where you progressively lose all your glycogen. Together with a moderate calorie restriction you end up losing some fat and an equivalent amount of water.
There's plenty of people losing 15 - 20 lbs per month.
Not only are my macros significantly skewed towards fats now, I am indeed consuming less calories (only 1000 cal/day of Ketochow) while still feeling satiated. My TDEE is ~2200 cal/day.
The actual range for the weekly calorie deficit is more like 1800 (3 pounds, 100% muscle @ 600 Cal/pound) to 17,500 (5 pounds, 100% fat @ 3,500 Cal/pound)
And if you are doing losing weight through calorie deficit with a basically sedentary lifestyle, the percentage of weight loss through fat is probably going to be no higher, and possibly substantially lower, than your starting body fat percentage. The key reason for working out while losing weight is maintaining muscle mass.
Less protein is converted to glucose than carbs but you can still eat too much protein and kick yourself out of ketosis. Fat converts to glucose at the lowest amount of the 3 macros.