He's an actor, I don't think he is a NVA (or more properly, especially now, PAVN) officer of any kind.
It may be that "Soldiers" is only a secondary concern, and the real concern is another of his roles(from the article lined above):
Vietnam has also taken issue with another movie role Duong took -- that of the head of a refugee camp in the 2001 movie "Green Dragon," starring Patrick Swayze.
That movie was about the life of Vietnamese refugees in a U.S. camp after the war in Vietnam ended in 1975.
"...both the movies carry the same tone of distorting the history of the just war of our people and the kind-hearted quality of the Vietnamese," the defense ministry-run daily said.
Communists can never stand being portrayed in their true light. PAVN solider, like soldiers everywhere, are just that soldiers, for the most part, aside from a few polical generals anyway. (And we've had a few of those ourselves, in fact maybe more than they do, at least prior to the Korean and Vietnam wars, think how many Presidents were Generals first) This does not include their equivalent of the KGB or GRU, even though those "people" and I use the term loosely, often carried military rank. Communists have never really held their own military leaders in partiucularly high regard, and certainly never trusted them.