In "The Three-Body Problem," a Chinese physics professor is attacked in a communist "struggle session," accused of teaching the theory of relativity, which "represented the black banner of capitalism." Did Chinese revolutionaries actually attack scientific principles as anti-communist?

While there's always more that can be said on this topic, you may be interested in reading these excellent answers which may address some of your questions:

/u/restricteddata responded to the question In the novel "The Three Body Problem" members of the "Red Guards" during the Chinese Cultural Revolution denounce certain physics theory (such as the Big Bang or quantum theory) as "counter revolutionary". Did this really happen and if yes why?
/u/theshadowdawn answered How accurate is the portrayal of Chinese cultural revolution in Cixin Liu's SF Novel "The Three-Body Problem"?