It's just that he was born unable to understand emotions.
Is that person embarrassed or insecure? Suspicious or curious? It's confusing when someone says, "Please don't hate me," but their face says, "You should definitely hate me for occupying the same planet right now because I wrecked your car."
Riley's life is filled with mind-numbing boredom until Henry arrives. Henry's amazing! Henry believes the world is populated by robots posing as humans. Visiting Henry's world is like being a tourist in a foreign land.
When police question Riley about Henry's disappearance, Riley lies about their dangerous game and scrambles to save himself from being named accessory to mass murder at their school. But if Henry talks, Riley loses.
When someone feels nothing, do things like loyalty, friendship, and trust really matter?