From the article you linked:Some are healed by radiation. Not all. Some.
Here is a Fallout wiki article on ghouls:
Ghoul | Fallout Wiki | Fandom
While ghouls require food and water, the regenerative properties of their mutated bodies can sustain them in the absence of either. In most cases, this coincides with the transformation into a feral ghoul. However, there are three known cases where prolonged isolation with no air, food, or water had no deleterious effects on the ghoul