Ignore the haters. Sports nutrition for teenage athletes is definitely I thing. My child (who was trying to gain weight for sports performance) had a few sessions with
https://rbitzer.com/team/blair-solberger/
The goal was to build out a diet plan that had enough calories, carbs, protein, etc, to fuel the athlete's body and improve performance - especially during adolescent years when they are growing. It was helpful.
Learning about nutrition and how to fuel an athlete's body is important and helpful information and really has nothing to do with an eating disorder.