Something in wall when trying to hang shelf?
You either hit a vent pipe, water line, or electrical wire. Considering it is a laundry room I would bet you hit the vent pipe as it is up high. Even if you punched a tiny hole in a vent pipe that is nothing to worry about. Water line is a different scenario. Look under the house in the crawl space for a water leak at that area. If none then you are ok.
hit a electrical wire in the wall ???
You probably hit a nail plate (protects electrical wires going through drilled holes in the studs). Search Nail plate to see what they look like (move the nail hole up or down at least 3 inches and you should be able to hammer the nail - if not find a new stud don't mess up what is behind the drywall.
you maybe found either the water supply line or the electrical supply
Electical wire. If you had damaged it, you probably would have received a nice shock. When I do that I use a stud finder to locate studs. Then I make a very small drill hole but I only go in just over half an inch, so I make sure if there is a stud there, or not.
Could be a person hiding in your walls