Corrupted image -- but who's to say if the card has a bad sector, the camera was interrupted somehow while writing the image, if power was temporarily lost, if the battery was weak or some one-time anomaly. With computers and electronics, you'll never now.
I would say keep an eye on it and see if it happens again.
Could be the camera. Could be the battery. Could be the contacts with the battery. Could be wiring inside the camera. Could be a transistor. Could be another chip.
I don't mean this to sarcastic. It's just too difficult to know for sure.