Apparently times have changed. When I was in Japan (1965) pachinko machines operated with metal balls.
I was there in 2014 and I can attest that they still used metal balls. I think what is meant is that the tokens are used to activate the machines.
The coin appears to say "shiyanpo" or "シャンポ" in the katakana alphabet. This could mean "Champ" or some other variation of those characters (Katakana is used for foreign loan words in Japanese). I've seen other Pachinko or gaming tokens use the same format. Is the coin the same on both sides? Many Pachinko tokens have duplicate sides.