If i bumped on someone's car is it necessary my car should get scratches too ? ?

well i took a small slow reverse of my car and brought car back to its parked place and after i get down and see that the car parked next to me , it has its backside door side's bumped into..i see my car's side and it doesnt has any scratches or abrasion marks..i am scared that did i bumped that car ? actually i took reverse very slow , so is it possible i had slowly bumped his car's side and the plate gone inside a bit ..is it done by me ? i am scared. is it possible my car did it ? my english is bad hope u get what i mean