Need Help! Accident

Ok, well today on the way to school i was coming up to a stop sign and this guy honks at me so i look over and i tell my gf to crank down the window and he yells out your muffler is raddling, and i had the clutch in.... and i bumped the guy in front of me at mayb 5mph about. So he has 2-3 scratches on his bumper, very thin scratches like being keyed and none of my white paint was on his car or anything like that... Heres the thing, i dont have a license plate in the front is it even possible to scrap his car with like a 5-7" small thin scratch perfectly straight and horizontal on his bumper? I got the ticket and all that stuff, but he told me before the cops came (ya it was a scratch why call the cops, i even offered him 250$ cash right there...) that he has been bumped into before a couple time before. I think the scratches might have been there b4 i bumped him... I will measure the hieght of my bumper and his tomorow, and post pics..
But I just dont see how i can make a perfectly straight horizontal scratch on his bumper, with out having a dent, and i have a very smooth bumper with no license plate in the front and its plastic and smooth too.... Is it even possible I did it?

My car: 90 integ hatch
his car: 2005-6 accord

i work for AAA claims and under your circumstances of he said she said, you will be held responsible. otherwise you still made physical contact by rear ending him, the favor is on his side. you can plea your case to the liability adjuster, but, you still made contact. if you have liability coverage, who cares, there is nothing to worry about but your premium increase next renewal :P