One wiper arm became loose, collided with the other wiper and ejected the wiper blade. Watch to make sure your wipers are parking correctly, if one is up it means that it is probably loose.
Open the hood and remove the plastic cap on the wiper arm end with a small screwdriver. Loosen the wiper arm nut using the apprpriate metric socket. Adjust the arm to the desired park position and tighten the nut, replace plastic cap.