I don't think he did. Private Martini (Mineo) heard something moving and challenged with his cricket clicker. The German heard the clicker and chambered a round - click click - so Martini stood up and walked towards him in the dark much relieved and BANG! Then the German chambered another round.
No, after the sound of the German chambering a round and Pvt Martini came out from cover, there were two shots very close together before the German appeared and chambered another round. I suppose the other shot could have been fired by another German, but we did only see one.