Answer:
It suggests that this sort of incident is commonplace.
Step-by-step explanation:
A Decade is one of the stories written by Ha Jin as a part of his story collection called Under the Red Flag. These stories tell about the lives of people during the Cultural Revolution in China. China's youth rose against old culture, habits, ideas, and customs. This period, which lasted from 1966 to 1976, was filled with violence. Ha Jin's A Decade, Ha Jin gives us only a glimpse of it.
Based on this information, we can conclude that Ha Jin's matter-of-fact tone in the given passage suggests that this sort of incident was commonplace. Violence was something that people were used to during the Revolution, and a teenage boy beating his teacher wasn't surprising.