This was about the famous Battle of Ap Bia in 1962 which was built up to show how bad the ARVN were. Vann wanted the tale told to boost the requirement for more US advisors and equipment (and to prove his assessment of the situation was right and the MACV staff appreciation wasn't. The press loved the story becuase it had all the right parts-dogged brave ground soldier, lying staff officers and generals, corrupt worthless US supported anti-communist forces. Sheehan realized later that Vannhad played him as he was trying to play Vann. Hence his censorious tone throughout his mega-epic. Van was shifty and frquently a snake but he could get things done in the snakepit of Viet-Nam. His unprincipled and unconventional methods is what the military establishment disliked. He wasn't any honor, duty, country boy scout but there are times when to defeat evil its not virtue that prevails but a fox against the stoats.
What is interesting, though, is how the journalists would latch on to ONE source (good or bad) and ONLY report what that guy said.
This was the famous David Halberstam/Marguerite Higgins battle, where she actually went into the "bush" and talked to villagers about Diem, and found out he was pretty popular, or, at least, not unpopular. Halberstam, writing almost exclusively from Saigon, only reported what the anti-Diem sources told him.