Although thousands Chinese words and expressions have been incorporated into the Vietnamese language, it still not a valid reason to say that Vietnamese language was derived from Chinese. why? apply the same logic, there are thousand of French words and expressions have been incorporated into the Vietnamese language as well but no one will claim that Vietnamese language was derived from French language. Although it might seems more logical to say that Vietnamese language was derived from French language because Vietnamese lauguage uses alphabet lettering, not characters such as in Chinese, Japanese, Korean,...,etc.
from what I've read, there seemed to be a consensus a agreement that Vietnamese lauguage was dirived from Mon-Khmer linguistic family.
Steve