[lvlrsSTI]

Is he partial or pure ethnic Chinese?
Thai decree in 1920 to have all minorities using Thai names if they want to register as Thai nationality.
So it is very hard to differentiate.    
Official number of  Chinese is 10-14% putting them 2nd largest group.
Thai govt consider Thai Lao people as its sub group of Thai people else Chinese would be third. 

If half gene or less and not following ancestry culture closely, should follow their father line, do not confuse people lah

40% Thais have Chinese blood. However Chinese Thais are mostly mixed with local Thais and assimilated to Thai society, which is different from the case in Malaya.