From what I understand, the 530 will also continue to fly on its assigned path until it self-destructs even after the launching AC loses lock. If the missile happens to fly close to a target, it will trigger the proximity fuze. Looking at the track, this may also be what happened.
I have been doing a lot of AA combat with the M2000 lately and have still not seen one instance of the 530 hitting a target after I lose lock, so it would seem to be a pretty rare occurence.