My mother grew up in Ipoh. Her brother was drafted by the British in the 1950s for this campaign (as was typical of British colonial practice, he is not malay, chinese or english). His and his buddys' description of the process was pretty clear: 1 - all bumiputrahs into kampongs. 2 - once that's done you are free to shoot anything that moved (which he said was a euphemism for ethnic chinese), with no consequences.

Allegedly the British were fighting communist infiltration from maoist China, so the shape of your body was proof of your guilt. I have no idea if there really was infiltration and the cantonese/fujianese who spread through the British empire were typically hardly of the communist persuasion.