It would certainly be disturbing if one's parents wished that on their offspring. But, then again, it is a fantasy story.
The adjective "disturbingly" is often used where the speaker wants to convey and even higher level than "extremely," perhaps to the point of being unsettling, disarming.
It is often simple hyperbole, like the girl in the Eagles' song "Life in the Fast Lane" being referred to as "terminally pretty."
- For Teachers