What amazes me about this is why didn't these pax realise they were boarding a longhaul 777 instead of a smaller 320/737. If they are seasoned travellers they should have also noted the flight number and destination at the gate. On the other hand how come there were two extra unaccounted pax on the Grenada flight? Also what happened to the Granada baggage when there were two 'no shows' for the flight?
This seems to have happened before but lessons haven't been learnt.
BBC News - Avios mix-up sees woman fly to Grenada, not Granada