It’s almost as though these battles are more Pokken Tournament than traditional trainer battles, which is still cool, but not as cool as a gym battle.
That said, a Pokemon battling doesn’t necessarily mean a gym battle is underway.
Furthermore, some of the posters on walls tease matchups between Pokemon, rather than trainers.
Pokemon gyms usually have a little more style than steel cages, and that Charizard doesn’t seem to be taking orders from any trainer in the abbreviated scene.