Here's why I'm curious. If Vietnam's education system is producing students with such mastery of so foreign a language, that says something impressive about Vietnam's education system and, by extension, about Vietnam. In a roundabout way, it adds credibility to the OP as well.
About myself: I just read HN, join English communities like Reddit, Quora. I try to travel but nothing much.
Regarding OP, his experience is just an exception. There are many other good or bad things in our system. And if you ask me, I will say the education in the U.S. is superior tbh.
Not better, just closer to an arbitrary standard that has been held up as 'correct' by some subset of academics (who are not, by the way, linguists, as linguists are too knowledgeable about language to try and define what 'correct' means).
I've been involved with many high school and college exchange students from Vietnam over the past few years and some students I've been working with recently speak English at the same level as native speakers with no discernible accent. One of my current students scored over a 2200 on her SAT. It's really amazing. From my experience, and from what I've been told, the emphasis on English language studies has increased within even the last 5 years in Vietnam. Each year, the students that I work with here in the US speak better English than the students from the year before.
Those are international schools. Their tuition are usually very high, and way out of the price range for most families in Vietnam. Normal schools where I live (Hanoi) only teach in Vietnamese.
We do have English class once or twice a week where we learn the basics of the language. But it does not provide us enough exposure to the language. To improve our language skills, we usually have to take extra classes after school.