Comment by berdario
Despite what the USA did in its invasion of Vietnam, not because of it.
Vietnamese are trying to not forget their history: https://en.wikipedia.org/wiki/War_Remnants_Museum
(I'm not sure how many Vietnamese actually love USA, vs how many don't... I just want to remind that different people in the same society might hold different opinions, and the sentiment is certainly not monolithic)
Vietnam had such massive population growth that there are very few people who even remember the war. On the other hand China was pretty much always ingrained into their “national consciousness” as a permanent massive threat.