That doesn't mean Judas didn't sin. Matthew 27:3-4, "Then Judas, which had betrayed him, when he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders. Saying, I have sinned in that I have betrayed the innocent blood..." The betrayal of an innocent person is a sin in anyone's book. No?
Yes, it is by prophecy that this happened. But, just because a prophet foresaw this event doesn't mean the person in the event is not a sinner in the event. He left and hanged himself. Not very good because he fell and his body was split apart on the rocks below.