This sentence is true ?

Hi everybody
This is a paragraph I read on the Internet.

The last is wonderful: the Vietnamese really are an exquisite people, exemplified by the young women who take us around the resort on bicycles. Charming and friendly, they are proud and happy as they tell us how they have just passed their English exams.

In that, the sentence is highlighted in red, they use "an exquisite people". Is it true? I know that "Vietnamese", at here, is a plural noun. But I don't understand why they use "an" for "people" instead of "the" or something like that to go with a plural noun.
I cordially appreciate your helps. Thanks

When referring to a race or nationality, such as in this context, people is used as a singular noun. It can be confusing, even to native speakers, because the word is almost always used as the plural of person.

"The Chinese are a very superstitious people." This is correct English.

To further confuse the issue, the plural of people in this context is -- you guessed it -- peoples.

"The many peoples of Indonesia speak over 300 different languages." Here, peoples refers to different groups or ethnicities of people within Indonesia. The sentence "The many peoples of the nation finally came together in peace" underscores that there are different races and ethnicities in the one nation.

Fish is similar, actually. When we talk about many fish in general, the word fish is both singular and plural. However, when we want to make clear that there are multiple species, we use fishes. ("The rift lakes of east Africa are home to all sorts of fishes.")

Things like this confuse even native speakers, so it's a good question to ask!

P.S. You wrote, "I have been knowing..." The verb know is typically not used in the continuous form, so simply, "I know..." would be correct. :)