Well the Vietcong often disguised themselves as farmers as they didn't have their own military-style uniform. This often made soldiers paranoid upon seeing them, as they didn't quite know if they were looking at an actual farmer or a Vietcong.
Remember that post when an veteran visited the battlefield in Vietnam and the tour guy who was a Vietnamese just popped his head out from the ground and the old man almost died? That's how most Vietnamese are
Also @rosalinas