Drawing from model is about being the kind of character that enjoys spending hours tweaking at tiny details and measuring measuring measuring. Anybody willing to sit 3 hours in front of the model every day can learn it, if he understands that he must measure.
Drawing from imagination like Kim Jung Gi on the other hand is about doing that every day most of the day since you were a little kid, and you probably need an innate ability to boot (and that might be some form of obsessive-compulsive disorder / autism...).