In brief
The system combines images instead of using a camera above the vehicle.
Useful to know
The 360° view described by Bosch uses four close-range cameras: front, rear and side mirrors. A control unit combines the footage in a general view around a virtual model of the car. [1]
This explains why the painting looks like a view from above without a physical camera above the roof. When parking, it helps orientation relative to lines, walls and curbs. Do not take the image for a direct measurement of each point: it is a processed representation. Checking the actual environment and constraints in the manual remains part of the maneuver.
Sources
For further detail and to check the information: