All studies about this are still too recent to have reached your common school. Teachers fall exactly in the age span of people that can't let go of their phones in an almost unhealthy way and probably were pretty excited, when they found this game online - to share with the kids.
Most teachers are aware how bad smartphones are, at least from the surveys I've seen. They're more skeptical of them than parents or children. I think this case is kind of an outlier.