A steering wheel should be dead straight after alignment is done unless the car is bent.
Nicked from elsewhere as I couldnt find the words: "Steering center is controlled by the front and rear toe settings, when setting steering center, the rear toe should be set first bringing the Thrust Angle as close to the vehicle centerline as possible. the steering wheel is then locked in a straight-ahead position in order to set the front toe."
Basically, your man hasnt set the rear toe properly, but has then used it as a guide for the front. Although the wheels are all relatively speaking pointing in the same direction, the steering wheel being off centre indicates that relative to anything other than themselves, they arent. Or something like that.