'Disturbingly real' means like something which is completely immoral or disgusting or which is something that you thought would never happen actually happens. I think authors use this expression to create drama or tension :P I hope this helps

Disturbingly real- means something that is not real, but looks so real you wouldn't know the difference between the real thing and the object. Ex: The movie corpse looked so DISTURBINGLY REAL that I thought it was a real body. You can use it when you use the word "very" but disturbing carries the emotion of being "scared" or "bothered" when you see the object.