DJHT - The only health information in the article says "A few youngsters with eating problems have a hormone disorder, but in this case it SEEMS that Lu Hao's family have simply fed him much more than he needs."
First, a look at his endocrine system wouldn't tell us if he has Prader-Willi.
They'd need to do a chromosomal analysis.
Many of the kids are not MR, or are intellectually borderline.
Mild MR or Borderline IQ can be fairly hard to diagnose in a three-year-old.
I know this from experience.
EDIT: Parents usually have to install locks on the fridge and cupboards with these kids.