I'm willing to guess....again this is just a guess, that the FMS was not programmed incorrectly. If this is true it's also extremely unlikely that the FMS was sending bad information to the instruments leading to the wrong airport.
The automation systems and the procedures in place to operate them are pretty robust and reliable making it unlikely this was caused by a failure of the automation and navigation.
I'm willing to bet (and maybe I'm wasting my time here but just for the sake of discussion) that this was purely a pilot error. One pilot probably said..."I have the runway and the other pilot may have just taken his (or her) word for it and gone alone for the ride.
In the United States (for the sake of our overseas colleagues) airline pilots routinely fly visual approaches but are supposed to (required) to still have the proper navigation selected and programmed but I can see how it's easy to become complacent and ignore this.
Some of you may say "I never would do that" but I've witnessed it myself. I was jumpseating on a nameless major carrier in the US many years ago and observed the crew of an MD-80 nearly landing on a closed runway.
The FO spoke up but the captain was confident he was doing it right and the FO said..."oh ok" and remained quiet. I then spoke up and agreed with the FO which was enough to make the captain look again and he sidestepped at about 500' (I was commuting into my home base airport so I must have been more convincing because from what he said I think he just took my word for it). It was night and there were men and equipment on the closed runway but for whatever reason the runway lights were on.
Both pilots had the correct ILS tuned in but ignored the increasing localizer deviation as they approached the runway. Not sure what the flight director was up to that night.
We'll never know if my presence on the flight deck that evening saved them or just helped the pilot avoid a last minute go around. My point is that it's a mistake that can happen to anyone under the right set of circumstances and the only way to avoid it is to fight complacency and really pay attention all the time.