That is all very interesting! It seems a bit hard to pin down exactly why they feel the way that they feel. It seems like it is just the complex way that history played out.
It's also interesting what you said about their beef with the Chinese. This weekend I was visiting family and I have a cousin who is married to a Vietnamese woman. She had a bunch of family around who were randomly talking smack about Chinese people. I thought they were just kidding, but maybe there is some real animosity there.
I think that when a neighboring country has been attempting to conquer your country for several hundred years only to get pushed back over and over again you probably start to have a chip on your shoulder about said people. I don't know the full history but yeah, the Vietnamese have a very fragile relationship with their northern neighbor. This probably explains a lot of why they always keep the Americans close and allow regular shows of US Naval might in the region.