It seems that they were boarding from an airbridge.
OK, I stand corrected.
Out of interest, could somebody who is familiar with Malaga Airport explain the references to the passengers being "stuck in a boarding gate stairwell", and the quote from one of them in the DM "I looked through the doors onto the airport apron and the plane had gone".
I'd have thought that, once on the departures level of the terminal, boarding the aircraft via an airbridge wouldn't have involved going down (or up) any stairs ?
Just curious.