Thats OK.
Hung us still the family name of Mr. Cao. Ask any Vietnamese. Cao is not a surname.Its a first name.
Cao =(髙)
More details here : https://www.popular-babynames.com/name/cao
https://en.m.wikipedia.org/wiki/Cao_(Vietnamese_surname)#:~:text=Cao%20is%20a%20Vietnamese%20surname,transliterated%20as%20T%C3%A0o%20in%20Vietnamese.