I think this passenger may have been telling tall tales to the beeb.
I don't think so, my friend is an FO with FR at DUB and its FR's procedure to inform cabin crew of an emergency decent via the Public Address system. So its not out of the ordinary for passengers to hear ''Mayday, Mayday - emergency decent'' after all the plane dived from 31,000ft to 9,000ft at 4,200fpm also in one of the busiest sectors of airspace in Europe I don't think it could be more dramatic.