its a gray area-- he's following too close, and the front of his car touched yours. Although you were backing up, you hadn't completed your turn, neither had the guy in front of you, so therefore he could have avoided the situation by allowing you to clear your turn, and allowing you to avoid an accident w/ the car in front of you.
Plus the fact that he drove away, indicates he might not have cared, damage, if any, was minimal, or maybe he had warrants or illegal items in the vehicle.
If he calls it in as a hit & run, he/she will have to explain why they left the scene... plus why the front of their car hit yours. If you keep quiet about backing up (i.e. not talk about it even on here), it will be up to them to prove otherwise. You don't have to lie, just remain quiet and don't take blame-- insurance companies will work out any issues with monetary claims... (they say to never accept blame anyway)
Was there a NO U TURN sign?
Nothing to worry about here...
PS: being it was a light impact, you could always claim you didn't know you touched his car... maybe it was a curb, pothole, etc.