The man's reaction was excessive
As much as it does not benefit us to tell the truth: Looking at your cell phone during class is rude!
A little girl from China paid dearly for it. Her teacher got angry when he saw her "check" her cell phone, instead of paying attention to the lesson. So, he made the student break her cell phone with a hammer in front of all her classmates.
The man's reaction was excessive, but now he knows for sure that he will have the attention of all the children.