Problem here is that Vietnamese used Han Zi in official writing system in the past. Han Nom words are created by Vietnamese elites, but were not permitted to be used in offical document or history chronicle text of Kingdom.
The word or name 漢 is existed from time of Han Dynasty ( 漢朝, 206 B.C.E. – 220 C.E.), not from northern Wei 北魏, this kingdom existed in China later on, 385 to 535. As I know it's Han Zhong, Han xui, two word is existed from ancient time in China. Han Dynasty created first idea about Han people from Zhongyuan. Chinese labelled his people following to the name of the dynasty Emperor who reigned the country. In case you dont believed that Qin Shihuang is Han Chinese in origin, Han Dynasty is first Dynasty of Han people. There is a reason why to day Chinese Majority people (92 % of Chinese nationality ) claimed himself as Han Chinese. Southern Chinese claimed their ancestor came to south from North China too.
So that the word Han 漢 is used in time of Nguyen Dynasty has a anonym to the majority people in idea to make different Han and Man, majority people and minority people in ethnicity.
Đại Nam thực lục (大南實錄) is the official chronicle History book of Nguyễn Dynasty, in the same stylish of Han van 漢文, Vietnamese Kinh people as was in majority ethnic, was called as Han people 漢 人 and Chinese immigrant was called Tang ren 唐 人, Khmer krom was called Chenla people and other people on Montagnag was called Man (moi in Vietnamese) people. Does it mean that Hua people in Vietnam in Nguyen Dynasty era is not sinized ?
when you like to talking about influence òf Chinese culture in Vietnam, I would like to quote here again What is "Binh Ngo Dai Cao" stated; 南 北 之 風 俗亦 異. The costoms of North (China) and South (Vietnam) is different (Phong tục bắc nam cũng khác).
using of term 漢 人 to the majority ethnic in Vietnam is not evident for that Vietnamese Kinh people culturally is sinized.
Chinese borrowed the word for example coca cola 可口可乐 has led to 可乐 becoming the common Chinese noun for all sodas. when coca cola and sodas is different.
I advise you to read "BECOMING ZHONGGUO, BECOMING HAN: TRACING AND RE-CONCEPTUALIZING ETHNICITY IN ANCIENT NORTH CHINA, 770 BC - AD 581",Critical Han Studies The History, Representation, and Identity of China’s Majority
8. Hushuo The Northern Other and the Naming of the Han Chinese" instead before further embarrassing yourself.
Do you or do you not understand what anachronism is?
If my descendants were ruled by Vietnamese and called themselves Kinh,that doesn't mean I thought of myself as Kinh Vietnamese,I would still be Han Chinese.
Han as an concept didn't exist in Qin Shihuang's mind of his contemporary,even the Jin called themselves 華 not 漢.
If it wasn't for nomads ruling China there would be no 漢,as the Xianbei literally thought the Han dynasty still existed therefore when they conquered Northern China the natives were labeled as 漢.
While the Xiongnu labeled their subjects 秦 after the dynasty.
The Xianbei never called themselves 漢 and tried to call themselves 華 even as going as far to call the Southern dynasties as 夷.
Which manifested in 3 ways
1.As an ethnic label for Sinitic speakers of Northern China
2.The fallen Han dynasty
3 A crude slang meaning the average man
While the Tang used 漢 as a nationality which applied to Xianbei/Han ie all the emperor's subjects while 華 was preferred.
Which manifested in 4 ways
1.The Tang as a political polity and its subjects
2.The fallen Han dynasty
3 A crude slang meaning the average man
4.The central plains as a toponym
The Khitans called themselves 契丹,the Tanguts used 番(Mi in their language).
This practice was revived by the Khitans and Tanguts who labeled the Northern/Southern Song as 漢 while Khitans referring to their own Chinese subjects as 漢 or 趙(due to the Song imperial household) and the Tanguts calling their own Chinese subjects Za which doesn't correspond with 漢.
While Northern Song had frontier soldiers referring to themselves as 漢 while literati and nobles disproved of this and Emperor Huizong even issued an edict banning referencing the Northern Song as 漢 or 唐.
While Southern Song no one retained the use of 漢, while 唐 was popular amongst the lower classes while the elite preferred 華.
While Jurchens also used 漢 for the native Sinitic speakers and for "Chinese" terms such as Chinese writing,language,customs,surnames,culture etc,while the Jurchens hated the term 番(unlike the Khitans,Tibetans and Tanguts)and flogged those who used it for them or their subjects/state.
So in reality 漢 was used as a substitute for Chinese dynasty,people and culture.
You are just a revisionist troll who seeks to underplay Chinese influence,漢 meant that the Vietnamese Sinicized,while your case of Chinese calling themselves 唐 doesn't work either as it was used exclusively for Chinese.
Why do you think terms 漢字,漢姓,漢方,漢語,漢風,漢地 all exist?
Are you seriously going to argue that 漢 isn't Chinese?