Good question. Stress can cause weight loss. Not anorexia. And depression too, of course. If Daniel was upset about a girlfriend breakup and about his mother's condition under the influence of her gang of "friends".....and about his future out in the world maybe.....all that could take a toll and lead to weight loss. But NOT to Anorexia....that would have to be a physician's diagnosis.
You're right - how would Stern or KE or Anna know what was Daniel's condition?