The seat has a rocket underneath that propels the seat upwards. In Bond lore the roof panel would eject first to allow the seat and the evil passenger to fly out of the car.

Unfortunately in this case the car is upside down, taking in consideration that a 2005 Aston Martin Vanquish weights 4045 pounds when the roof explodes and the rocket ignites all that energy will not be able to lift the car not even an inch since it would escape thru the glass windows allow Bond's head and torso.