Firstly check the bumper alignment, make sure that the fitment is straight and true. Check your rear light clusters are secure.
Get under the car and check all the brackets also Depending on where he hit I would also look at the exhaust tips for alignment also.
As the bumpers are plastic, they do have some flex and durability. You should be able to see where he hit from scuff marks/cracks in the paint/bumper (depending on how hard he hit you).
I hope its all ok