In cold war, China is a dirty policy smuggler, helped Vietnam to take position to bargain with our enemy.
Don't forget that Zhouan Lai is secretly negociated with France in back of Vietnam in Geneva 1954, and making pression on Viets to get favor of France Colonial, aggreed with France on discuusion that two part of Vietnam will be divided from 13th moved up to parrarel to 17th parrarel. China showed of her true face.
Vietnam was trapped and loser after 1954.
China did same tactic again with Vietnam from 1968 when China reduced support to 1972, when you signed with US in Shanghai the document stated that" China agreed that to keep the situation in region unshanged,... " it mean Vietnam will be divided for ever and Taiwan is still under protectoriate of US, in exchange China could normalization with USA. Note that, after bittery lession 1954, we don't let China involved in to Peace Conference in Paris.
In Vietnam war, biggest help belong to USSR and socilist countries, not China. However Vietnam tried to take a neutral position between China and USSR spliting. But china is backed Khmer Rouge to attack on our back, to making dirty policy against Vietnam again.
Vietnam is not puppet of China, not only could fighting for China interest. The cold war is dead. such kind of voluntary help is fake, China did it in the past is for China her own interest.
We have defend our national interests.