The fact that they boarded to Bodrum flight was because their boarding cards said Bodrum and they, and their bags, were checked in for that flight.
I can assure you that despite what the article said, it was not a comment check-in. The Arrecife and Bodrum flights were checking in next to each other, but on seperate desks. - Error No.1 - passengers in wrong queue.
These passengers at no point looked at their tickets that they collected on the day. Their tickets would've stated Arrecife, and the Arrerfice flight number. - Error No.2 - passengers did not check tickets were correct .(A requirement by the airline whether tickets delivered before hand, or collected on day) and did not note down destination and flight number, whose to say there wasn't more than one flight to Lanzarote on the same day.
The agent unfortunately did check them in onto the wrong flight, however there was plenty of oppurtunity to have spotted this mistake well before getting onto the plane. - Error No.3 Agent did not check tickets correctly and manually entered names in system
Experienced travellers check everything because they're scared of messing up,
Inexperienced travellers check everything because they are scared of messing up,
Error No.4 - passengers took boarding cards, put them away and didnt check any details.
I for one find it very hard to believe that all 3 passengers fell asleep straight away, missing any annoucements from crew or pilots. Pilots normally comment on their routing, weather on the way and estimated arrival. This is also backed up by the live map on the screens. Alarm bells should've rang when they noticed they were going East instead of South.