Why would they be armed? They were on an airfield that had been taken and secured, and from which IJAAF aircraft were operating. No need for everyone to walk around armed to the teeth.
Sungei Patani, where 21 Sqn had been based, had not been defended at all. The Japanese had conducted a secondary landing on the west coast of Malaya, while the main force drove south from Siam, supported by the main landing force on the east coast, applied constant pressure on the limited Allied ground forces in northern Malaya. There was simply no way the Allies could have retaken Sungei Patani.
Regardless, we don't actually know when the photo was taken. Even a few weeks after the Brits evacuated Sungei Patani, the front line was far enough south to have obviated any need for active defence by the IJA of any airfields they had captured further north. The IJAAF put huge numbers of aircraft into Sungei Patani, as shown in a RAF PR image that was probably dated from mid-December 1941. They wouldn't do that if Sungei Patani was at risk of recapture by the Allies.
I do not know your army, but most i have read about do not like to have troops carrying when enemy is not near.
So these guys do not even hold a pencil knife. Front long gone i would say.