what you're describing is a mental deficiency or illness. Being able to understand emotional state should be considered normal human behavior.
Doing math, or telling a joke, or catching a ball, or carrying a tune are all normal human behaviors. People's skills at any of them vary, and we don't refer to those with lower skill levels in that category as mentally deficient or ill.
Doing math, or telling a joke, or catching a ball, or carrying a tune are all normal human behaviors. People's skills at any of them vary, and we don't refer to those with lower skill levels in that category as mentally deficient or ill.