Not an Airbus man .. but the story will involve a failure of the system, not crew erasure. .. ie the record was either absent or corrupt, rather than deleted. Not at all uncommon as most operators don't routinely extract data from the DFDR .. those who do pick up this sort of problem and can fix it. So for example, I have one hull which has some spurious DFDR problems ... will take some time to sort it out but it will get fixed in due course.