The events that you are referring to happened 50 years ago. The median age in Vietnam is 32. The vast majority in Vietnam would not know what you are talking about. Putin's popularity in Vietnam, India, and other countries containing 80% of the world's population that are completely ignoring Western “sanctions” has very little to do with events that took place 50 years ago. His current popularity is because of perceptions formed much more recently.
“The events that you are referring to happened 50 years ago.”
And Russia continued to fund and support and supply Vietnam for many years afterward.