It could be as simple as cosmic radiation that flipped a bit (it has happened before: https://www.independent.co.uk/news/science/subatomic-particles-cosmic-rays

It could be as simple as cosmic radiation that flipped a bit (it has happened before: https://www.independent.co.uk/news/science/subatomic-particles-cosmic-rays-computers-change-elections-planes-autopilot-a7584616.html https://www.independent.co.uk/news/science/subatomic-particl...), or as sophisticated as an adversarial hacking.