Champ: Y'know how they say teenagers have no fear of death? That they're never gonna get hurt? Well not me, OK? I was born with the gift of fear.
R.L. Stine: All the monsters I've ever created are locked inside these books. When they open.
Hallway Player: Hello, Mr. Stine.
R.L. Stine: Hello, Mr. Black.
Zach Cooper: She's locked in this house and her dad's a psychopath.
Champ: Does she have a friend?
Slappy: You have the right to remain... silent.
Answer: When they use the term "monsters", it isn't specially about evil creatures, it's anything R.L. Stine created in his books. All of Stine's creations were pulled into the book, including Hannah, who was never a real person. A ghost would be considered a monster, no matter how friendly or benevolent.
Bishop73