Exactly, you got it right. In fact as i said before, had it not been for China(and to soe extent Russia/U.S.S.R), North Vietnam would have been decimated in a few months at most by the U.S and its south Vietnamese allies. It was China and Russia support that kept the war going for so longggg. Also the U.S was afraid of launching a massive ground invasion of north Vietnam since it was too close to China's border, and the U.S was afraid of repeating a Korean war, since they thought by launching a massive ground invasion of the North, this will provoke a direct Chinese intervention like it did in Korea earlier, in support of the the communist North Vietnam.
So Vietnamese should blame China for their current Communist authoritarian government.Since had it not been for China, Vietnam would have been a democratic prosperous country under the U.S by now, and would have avoided all the long vietnam war and subsequent sanctions/isolation that followed. This would have made it easier for Vietnam to be ally with the U.S and Japan together with some ASEAN countries as well. But the Communist North Vietnamese Victory over the South/U.S with massive Chinese/Russian help prevented this from happening unfortuntely.