My hunch would be that he became distracted and intimidated by the controller's message to stay clear of Cherbourg restricted area. Whilst in descent he may have decided to disengage the AP to make a manual turn to the right to avoid the area. Feasibly quicker & easier to do this for a few moments rather than mess up a GPS flightplan by altering the AP to HDG. Perhaps coming from a high speed AP controlled descent into a manual turn could have induced disorientation and panic.
For the sake of arguement, the radar picture looks like the work of an AP, at least I couldn't fly that straight manually!