Vietnam is definitely neutral to both parties. They can't afford to pick sides at all. In fact they have a 3 N's policy: no foreign military bases, no alliances, no aligning with one country against another.
I'm not sure where you get this idea that they are US aligned. This is specifically against their policy. They play a very balanced game as they should given their big neighbour...
https://thediplomat.com/2019/01/vietnams-defense-policy-of-n...