Both my current and previous cars had specific +tive and -tive charging/jump start terminals under the bonnet; but then they both had the battery hidden away in the depths of the boot.It's pretty close to the battery in that picture, just that bar. Probably back EMF and all that why they have it connected to the chassis and not directly to the battery. Normally you put on the battery. With all the electronics in the car they are going for the straight earth. Let the physics people contemplate that piece of metal ?.