Though I dont like vietnamese to have any link with chinese, but honest to said the Vietnamese has similar look of the ancient Hans than modern Chinese which mixed alot with manchus and mongol. Cantonese for example still preserve tha ancient han chinese looks. Alot people mistaken north vietnamese look similar to Han but the fact is southern vietnamese are more of having the looks of ancient han chinese take into consideration the history of its creation that is where most chinese migrate after the clloapse of Ming Dynasty. Like the cantoese they are merchants excel and their culture are most influencial in Vietnam like the Hong Kong of cantoese influence in China.
The north Vietnamese although it was origial Viet state but the much influx of north Chinese migrant during Qing, then whole load of Tai and Hmong migration this makes it no ancient. Similar to mongol and manchus they are good at fighting but they suck as merchant, their culture is also easy supress by southern vietnamese culture.
Pay more attetion you would notice Cantonese and Southern Vietnamese look similar in many aspects, the only different while Cantonese mix with northern chinese (mostly manchus, mongol, ...) the south vietnamese mix with Khmer.