Why would the apostles have asked if premortal sin was the cause of a man's blindness at birth?

John 9:1-2, "Master, who did sin, this man, or his parents, that he was born blind?" Why would the apostles have asked if premortal sin was the cause of his blindness at birth unless he existed in some capacity before mortality and, in addition, had the capacity to sin in such pre-earth life?