The same thing happened to me when leaving the garage and reversing, out of nowhere the car blocked and a red warning appeared on the active info display, I couldn't read what it said were seconds "I was worried if I hadn't damaged the car".
From the camera I saw no obstacle but as my cat appeared in front of the car I always assumed that it was he who had triggered the braking.
My Polo GTI has manual gearbox, so I also confirm that it works the same way as the DSG.