This guy obviously has no idea what he is talking about. The only way your body would be eating lean muscle is if you are not getting adequate protein, which is unlikely if you are eating meat at every meal. Also, even if you didn't have adequate protein you would still be losing mostly fat because you need to lose 50 pounds.
Carbs aren't necessary for workouts but they might be helpful. The best way to figure it out would be to experiment. Maybe one day eat a sweet potato an hour or two before you work out. You might have a better work out, or you might not.
Could you post your meal plan?
Anyway, I can guess his response. He will say that you need to eat grains and you are eating too much fat. Neither of these are true really. Basically he has absolutely no idea what he is talking about like the great majority of personal trainers (at least when it comes to food).