He’s basically right, you can cut with keto and intermittent fasting. It’s safe and effective. But in general dry fasting doesn’t hurt the muscle mass much. Your HGH gets triggered and muscles get protected. You can also build/rebuild muscle easily with that regimen. Rolling stuff also will work fine. Muscle mass gets consumed when your body has no other choice (fat). Water fasting might be less effective at preserving muscle mass.
Strength wise, you will lose some at the beginning, then regain it on a good diet. Keto is fine