I suppose the difference between "tieng Viet" and "nguoi Viet" is the difference between the Vietnamese language and the Vietnamese ethnicity?
Yes, you are correct.
Tiếng = voice, sound, language.
Người = people, human, person.
Why "người Việt Nam" instead of "người Việt"?
Both are correct. We often use "người Việt" for short. Same with "người Nhật" and "người Nhật Bản", "người Hàn" and "người Hàn Quốc",...
I've heard that "người Việt" refers to "Kinh people". They account for 86% of the Vietnamese population, so the expression "người Việt" might exclude the other 14%. It's only my opinion though...
Ko con dê
Việt Nam ơi , Việt Nam ơi
Isn't the name of this module "Questions 1"? So why are we getting a sentence which is not a question and has nothing in it specifically that is used for constructing questions in Vietnamese?