Why China Kept Quiet

Dr. Kissinger had asked China’s P.M. Chou En-Lai to attack India across the NEFA border.
The Soviet buildup on the Sino-Soviet border on the Amur river border (of almost 44 divisions from the normal 3 or 4) kept China out of this conflict.
Recent declassified documents reveals a second factor: the feud between Chinese Communists, assassination of Chinese Defense Secretary on China-Soviet border and sacking of Chinese military generals also stopped Chinese intervention in India.