It began as a purge of Communists and turned into an ethnic cleansing of Overseas Chinese. The Communists were mostly Chinese. Sukarno had used the Communists to hold power and would have ultimately lost Indonesia to them if he had continued to rule. Indonesia in 1968 was very much part of the Viet Nam War.
Ethic Chinese disguise their roots with weird names like Soeryadjaya to blend in with their dangerous hosts.