The numbers are consistent with some kind of fume release in the rear-crew rest area. Is it possible that something went wrong there and assistants from unaffected attendants who descended into the area also got sick. Only those pax close to the crew rest area entrance may have been affected.
As the crew rest area in the a380 is downstairs it might allow pooling of fumes from cleaning, disinfecting or insecticide that might affect the first 'off duty' team down there.