I think that story has been proven false tho the Russian sniper was real and really did kill a lot of Germans.
Major Konig was the german sniper sent to kill the russian. Zaitsev and his spotter Nikolai Kulikov were stalking the german along with a communist political officer who was there to witness the historic event, and was wounded.
It was the next day when Zaitsev offed the german after waiting all day to spot the scope reflection.
Zaitsev was credited with 242 kills during the battle of stalingrad, and eventually had accounted for 400 kills during the war.