Warning, I have not seen the movie. However, severe emotional stress is capable of disrupting a child's growth resulting in a short stature completely separate from a person's genotype or actual level of nutrition.

It goes by several names: Social dwarfism, Psychogenic dwarfism or Kaspar Hauser syndrome. It's very rare in the general population but not uncommon in children who are abused or in cases of feral children.

It's typically defined as an abnormally low level of Growth Hormone (GH) as a reaction to stress. I'd have to dig out an old neurology text book for the nitty-gritty, but in essence, GH is released by the anterior pituitary gland which sits below the brain. Secretion of this can be disrupted through extreme stress. So people present with this condition looking like a more typical GH deficiency. If the emotional stress is removed, then normal growth can then resume.

Now, this is a syndrome of arrested growth which can then be restored. This condition would not cause a decrease in height or size from a person's original size. For a person to actually lose any height would require more than emotional stress. Starvation or other nutritional disruption can result in osteoporosis or osteomalacia which can reduce height secondary to microfracture in a person's vertebral bodies, increased kyphosis or other orthopedic problems. But this is more typical with a genetic disorder or long term malnutrition rather than a short episode of disrupted nutrition.