its not an expat school, its a private school teaching foreign curriculum so the students from there can go to foreign universities. They do not meet the eligibility requirements to take gaokao.
it is easy to see why he would be upset tbh. His life, though physically in China, is spiritually in the west. His kids attend a western school that is barred from gaokao. He has, against their will, put them on a path towards only being able to go to school in foreign countries.
His salary is paid by white finance bros. His interests lie in exploiting the Chinese people and the infrastructure, environment and institutions that Chinese people have built. In fact he is even worse than the white finance bros. For them, exploiting China is just business. When they can't do it anymore, they talk some shit then leave. For him, getting a pay cut is like losing his parents, it is a personal affront. His parents aren't the ones paying him 500k RMB per year.