The wording is a bit awkward, but if you re-read what he wrote, it's not what he's saying at all.
Because a ketogenic diet depends the amount of carbohydrate restriction that will cause your body to physiologically be generating ketone bodies (eg, say less than 20g of net carbs), even at a constant formulation that doesn't change (as your TDEE changes) you will still be in the same state of ketosis - eg, if you measured your mmol concentration of BHB, it would likely remain the same. However, your caloric deficit of course would change (and you would need to lower it to match that to maintain your rate of weight loss).
In your hypothetical example, if your TDEE were 2000kCal and you were able to eat and absorb 4000kCal of butter a day, you would gain weight (although slower than the expected 0.57lb/day due to increased TDEE; this expenditure change (up to +50%!) was shown in the Vermont State Prison overfeeding experiments in the 60s). But despite that, due to the complete lack of carbohydrates, this diet would definitely stimulate ketogenesis (and would do so regardless if your TDEE were a 2000kCal surplus or deficit).
Due to the complete lack of proteins, you would eventually start consuming some lean body mass to produce some of the glucose (a percentage of glucose would be provided by the glycerol molecule holding together each triglyceride) required by the brain (~30%) and RBCs. I'd expect a pure butter diet to have about the same physiologic effect on protein-sparing as an extended fast (eg, you'd probably last a couple months before eventually expiring).
Because a ketogenic diet depends the amount of carbohydrate restriction that will cause your body to physiologically be generating ketone bodies (eg, say less than 20g of net carbs), even at a constant formulation that doesn't change (as your TDEE changes) you will still be in the same state of ketosis - eg, if you measured your mmol concentration of BHB, it would likely remain the same. However, your caloric deficit of course would change (and you would need to lower it to match that to maintain your rate of weight loss).
In your hypothetical example, if your TDEE were 2000kCal and you were able to eat and absorb 4000kCal of butter a day, you would gain weight (although slower than the expected 0.57lb/day due to increased TDEE; this expenditure change (up to +50%!) was shown in the Vermont State Prison overfeeding experiments in the 60s). But despite that, due to the complete lack of carbohydrates, this diet would definitely stimulate ketogenesis (and would do so regardless if your TDEE were a 2000kCal surplus or deficit).
Due to the complete lack of proteins, you would eventually start consuming some lean body mass to produce some of the glucose (a percentage of glucose would be provided by the glycerol molecule holding together each triglyceride) required by the brain (~30%) and RBCs. I'd expect a pure butter diet to have about the same physiologic effect on protein-sparing as an extended fast (eg, you'd probably last a couple months before eventually expiring).