I would guess the shutter in the lens has accidentally fired on its own, without the camera firing it. This is a common issue. To solve it is fairly easy. Look into the back of the camera at the rear of the lens. You'll see a flat-head screwdriver type slot. There is a red arrow circling around it--this signifies the direction yo need to turn the screw. It will cock the shutter if you turn it all the way and all will be well.
There's open rather major footnote here. It takes a fair amount of force to turn the screw and the thing is way down inside the camera body--there are lots of stories about people trying this and the screwdriver slips out of the slot, under force. Guess whaere the tip of the screwdriver lands? The rear element of the lens is right there, waiting to get dinged.
You can do it if you are careful--I've done it any number of times. Better yet, go on e-bay and buy the specialized tool. It won't slip out anywhere near as easily and only costs a few bucks.