So right after he published The Things They Carried (in which O'Brien told us that he'd gone back to Vietnam, which wasn't true), O'Brien actually did go back to Vietnam. Then, in 1994, he published a short story in The New York Times about a guy who goes back to visit Vietnam and then completely freaks out. Story-truth? Happening-truth? You decide! (source).
Apparently, most Vietnamese people haven't read The Things They Carried, nor do they find American accounts of the war all that compelling. Not because they find Vietnamese accounts so much better – they don't – but because they're not really interested in the war. Huh (source).