The Viet Cong were client states of the Ruskies, not China.
Vietnam has a long history of hatred for the Chinese.
Kissinger was playing an angle on the Soviets with China, neither of who really cares much for each other.
That’s what Nixon’s opening China was all about.
So OK
300,000 Chinese troops and advisors. $160 billion in aid ( in current value) constant movement of troops and supplies across the borders ( we watched this with no interdiction in China) and the Chinese shooting down over 5,000 US aircraft out of over 10K US losses….was a symbol of mutual hatred between China and Vietnam
Got it