It's possible. Look at
this thread... poor guy !!!
Pull out the tail light sockets like you're changing bulbs and see if there's water in there... or if the sockets are corroded indicating there has been water in there.
I doubt a collision described as a "bump" woudl cause a leak.... but you never know.
You can climb in the trunk with a flashlight and have a friend (a real friend... one who will let you out of the trunk) run a hose over the trunk seals while you look for leaks. You may want to remove the plastic and pull back the carpet first so you can see.
Not sure where you live, but don't do this on a 100 degree day in the direct sun because it can get hot in there !!!!! Fold down the rear seat if you can.