Chinese is spoken in Southeast Asia. Were their ancestors from China?

Southeast Asia is a region where China immigrates. Since the Song Dynasty, a large number of Chinese immigrated to Southeast Asia, so the proportion of Chinese in Southeast Asia is very high, accounting for more than 76% in Singapore and more than 30% in Malaysia.

The Chinese even established their own country in Southeast Asia and once became kings of several countries. For example, King Zheng Xin of Zhenwuli, Thailand is an immigrant from Fujian. Several dynasties after Vietnam's independence were basically established by Chinese.