In "Seventy-Six Dollars," how does Monk imagine he got superpowers?

He imagines he is riding in the car with his family, listening to Harry Potter on tape, when his dad falls asleep for a moment. His mother wakes his father up in time to avoid any serious catastrophe, but Monk manages to bang his head against the armrest in front of him. Later that day, while eating ice cream, he realizes he can hear his mother and his sister's thoughts.