According to the news online (if it is true) he is notorious for going missing without notifying his security team (mentioned by ex Royal security), or telling security that he doesn't need them! (He is as stubborn as the Queen refusing to wear a riding hat and going out on horseback with just a headscarf on.) When security discover he's gone off, they race after him, hence I suppose that is why they were further back when he rolled the car. This is all according to the ex Royal security guard.
If it hadn't been an armoured well-protected 4x4, he probably would have been killed. Unfortunately for the women in the Kia, it was probably like hitting a tank.