Incidentally, the stockholm station maybe not near a airport, but it doesn't mean the train or trains at said station could not have reached the airport, as the Arlanda express leaves Stockholm central to get to Arlanda airport. Its abit like the Manchester airport train in the UK goes well...from Manchester Airport to York and eventually terminates in Middlesbrough.
For all we know it could be a extended trip from when they went to visit Steam in Luxembourg which incidentally they could have got to via France on the ICE then caught a plane to Arlanda .