'Stale green' - has been green for a while, no traffic going through. I see it actually turned yellow just as the rider crossed the line. Crossing traffic won't see any traffic and may miss their red signal. I'd bet that happened in this case. Usually on a fresh/active green with cars going through, the cross traffic sees the motion and figuresout that they have a red and that if they don't stop, they'll wreck.
Assuming the lights were functioning properly, since the rider had the green/yellow, then under fault determination rules, the car was at fault. By being a little more dilligent at the stale green and watching for inadvertent cross traffic (looks like visibility was hampered by the hedge...) then the rider may have prevented the grevious bodily harm to himself, regardless of the fault.
They usually cover 'stale greens' in the M1 course? I did that a long time ago though...