chapotraphouse

This appears to be from a paywalled FT article but the author is given on the Vietnam category page:—

A new reality began to dawn’: the fall of Saigon, 50 years on
Chris Mullin describes the last days of the Vietnam war and the aftermath

I'm assuming there aren't too many Chris Mullins who are journalists writing about Vietnam and, therefore, he is the former MP with a Wikipedia page that gives this context:—

Having reported from Cambodia in 1973 and 1980, in 1990 he was outspoken on the British Government's record in Cambodia, being a leading voice in some of the first protracted debates on Britain's provision of clandestine military support to Khmer terrorists, allied to the Khmer Rouge.

and

his politics shifted leftward in response to the Vietnam War

and

He has been highly critical of the American strategy in Vietnam and has stated that he believes that the war, intended to stop the advance of Communism, instead only delayed the coming of market forces in the country

This doesn't read like ignorance to me. Like a lawyer prompting a witness, this seems like someone asking the questions that allow the interviewee to give the most effective replies.

I can't read the "reply was devastating" line as being personally devastating to an ignorant journalist, because someone in that position didn't need to write that and put it on show. Instead I read it as being devastating to the naive sentiment, perhaps held by the reader, that Vietnam's only legitimate response was to run to the UN.

The author has an extensive history with the topic and doesn't appear to be blindly anti-Vietnam, so I think you may have the wrong end of the stick here.