There's a lot of missing information. From the article:
"Yet they managed to land the plane without incident, and accompanied by emergency teams, it taxied off the runway and came to a halt, whereupon passengers watched as the two men were driven in an ambulance, said Der Spiegel magazine."
That appears to be saying that emergency vehicles met the aircraft upon landing, and instead of going to the terminal, it stopped mid-field and the two pilots were taken away via ambulance with the passengers still aboard.
If that's the case, it would seem that an emergency would have had to have been declared prior to landing in order for emergency equipment to be there, and both pilots being ambulanced away with the passengers still on board midfield would seem to create enough of a ruckus that an investigation would have followed. It would seem that the coverage in the media alone would have been enough to catch the attention of the authorities, regardless of the spin that the airline put on it when reporting.