Basically, during the spring/autumn and warring states period
times, the people that dwelled in the southern region of what's
called "Zhejiang", "Fujian", "Guangdong" provinces today and
northern part of "Vietnam" are called "Yue" people. The Yue people
are quite diverse and have many clans and tribal federation. The
Yue people are considered by the civilized chinese of the central
plain (´) as uncivilized and therefore barbaric. Because of so
many clans and tribes, the Yue people are also called the "Hundred
Yue or Baiyue" (Sz).
So the offsprings of coolies and uneducated hardship labourers make
up the majority composition of SG Chinese. These chinese are not
pure, intermixed with northern Hans. They belong to the Southern
strain, their DNA is very close to Vietnamese, hence the looks too.
You can even tell today that Cantonese have a lot of austronesian
blood and can often pass for Vietnamese or even Filipino, and can
look very different from Northerners. The same goes for Fujianese
and other southern territories.