crossed wires
Marcel; The incident you are referring to was caused by the fact that the technicians had to replace the electrical connector that the ELAC computer mates with in the electronics rack. When installing the wires in the new connector, several got crossed, causing the captains stick to command a left vs a right roll, and vice versa.
The flight control surface position indications on ECAM are directly displayed from position transmitters on the surface itself, not from whatever is being commanded by the stick.