How are they confirmed? I guess the water starter is leading to it, but the fire starter would need to evolve its head back closer to first form in order to fit that final form design we've seen in the leaks. Those leaks probably were real at the time, but not the finished designs.
At least in the video, it was still Ash Greninja (well, his Japanese name).
Not sure if that rly matters we've had mid evos look quite different from their finals. Like dewott to samurott, I remember thinking greninja was fake initially when leaked cause he looked so different from frogadier.