It is a cast fake, it was made by a German bank called Sparkasse and they are very common.
I do not know how it was possible to obtain them.
...
In 1971 or 1972 as child I participated in a "Sparkasse
Youth Olympic Competition" (Sparkassen Olympia-Jugendpreisausschreiben) related to the upcoming Olympic Games in
Munich. I won a copy of the Athenian
tetradrachm and a copy of a small African drum (I never knew what the drum
had to do with the Olympic Games)
I was so fascinated by the
tetradrachm that I knew that as an adult I would buy a real one. It took about 40 years until I did it