In anorexia recovery, my dad is obsessed with calories that I eat, why?

Obsessed? When people with anorexia are living at home with parents, ongoing family patterns are usually part of the eating disorder -- and family therapy is part of treatment. I agree with dr. Fowler that your dad is likely very worried about you, and his monitoring your calorie intake probably goes along with that. However, your ultimate recovery depends on what you do to nourish yourself, or not.
My guess is that he. Is very concerned with your health ; well being. This would be especially true if your anorexia became life threatening.