No, "Pokémon Arceus" movie is not the only movie that worked for the event.
The event you are referring to is the "Pokémon Arceus" event which was distributed in Japan via a special code that could be redeemed in Pokémon HeartGold and SoulSilver. This event allowed players to receive a special Shaymin with the move "Seed Flare".
The event was tied to the release of the "Pokémon Arceus" movie, but it was not limited to the movie itself.
The code for the event was printed on promotional materials related to the movie, including tickets, posters, and other merchandise.
Therefore, the movie was simply the promotion vehicle for the event, not the only source to get the code. You could have acquired the code from other sources, even without watching the movie.