It's a term like "put some meat on your bones".....they say it to let you know that they know that you haven't been eating well & that you are too thin or that they have noticed that you are loosing weight......but it's meant in friendly terms especially if they don't know you have ED issues.

When I have been stressed, & not eating, my friends tell me similar things & living alone, they usually even try to give me food to take home that will be easy to heat up & eat & not take too much of my energy to prepare.......

Sounds like your T is just caring...but if you have ED issues, you need to discuss it with your T even though the topic is uncomfortable.