My guess is that these cases are dysfunctions with aspects of the growth / maturation process, rather than outright stoppage of aging. If you look up images of Nicky Freeman, the 40-year-old referenced in the article who "looks like a 10-year-old", he in fact looks more like a 40-year-old with the size and stature of a 10-year-old:

https://www.google.com/search?q="Nicky+Freeman"&um=1&ie=UTF-...