This points to pilot error possibly induced by misreading of or faulty instrument readings.
What makes you think the pilot was controlling the aircraft? Airbus has a TMR computer system controlling it and false airspeed and/or pressure data could have given the system a nervous breakdown, as apparently happened to another Airbus off Brazil.
You might be interested in reading about the infamous Airbus crash at the Paris airshow. In that case, the computer crashed the plane while the test pilot was trying to stop it from doing so.
If I recall correctly, the pilot wanted to change altitude due to a large thunderstorm in his flight path. The updrafts in those conditions could have pulled the plane upwards at a high rate of speed. If the pilot then over-compensated, he could have put them into a dive for which there was no recovery.