He may be right about the unlimited calories from fat. I haven't been willing to test that theory myself. I try to keep my intake at least to seemingly reasonable levels. Especially when you consider protein, glucogenesis, ect., that goes along with all that meat at some point.
That aside, while you may be able to lose weight without exercise and while eating a ton of fat (IF he is correct), you still won't reach your full potential. Exercise would still probably boost your energy levels, make you feel better about yourself, and boost your immunity. Weightloss is not the only reason one should exercise.