The reason I would imagine is that Vietnam favours the United States at the moment, irony of ironies. I expect they didn't want him makng anti American statements. Vietnam is surprisingly pro American these days.
He missed out on an interesting visit. That museum is fascinating and intriguingly the American equipement (uncrashed) is better looked after than Migs and the like. There was an immaculate Huey there with obviously spurious USAF markings. It was obviously recently retired from service. I saw several Hueys still flying for the Vietnamese military. At the gate the MiG 21 is deteriorating fast.
The wreckage is fascinating and you can have fun trying to identify the bits. There are parts of F4's, B26's and a French F6F. The most poignant exhibits are helmets and personal effects of downed aviators. You have to wonder what happened to them.
Yes Chavez was put in his place by the Vietnamese.
