He's probably just not that anal over his car- I've done the same thing, been bashed from behind and not got all het up over it- was it an old car? This is one reason why people, particularly in London, use 3 or 4 hundred quid cars as daily drivers, you're going to get the odd dent or scratch and if you get steamed up over it and go running to the insurers every time it happens you'd kill yourself with the stress!!
I was hit on Stratford broadway- I think the chap who ran into the back of my car thought I was going to kill him, but it was only minor scratching and it's only a car, so I just told him not to worry and left.....lifes too short!!