I agree with the mass hysteria suspicion The fact that no passengers were involved when there were 400 of them on board the 380 and yet none reported any symptoms is simply not a sustainable alibi for the cabin crew's explanation of an on-board toxic fume event.
Along with the prior food ingestion explanation for the origin of the hysteria, there may also have been the possibility that some pollutant in the air in the crew bus that took the crew to San Francisco airport from their hotel may have been a cause of some of the cabin crew's subsequent symptoms. Or maybe something from the hotel itself affected them? The early days of the exploration of the causes of Legionnaire's Disease have a similar Sherlock Holmes-type series of conjectures as to the origins of the ailment.