Bastards.
Use of edged weapons and swords had a preferred religious symbolism to the Japanese.
Bruce Gamble, a historian who has done extensive research on Rabaul, actually dates the massacre to have begun on February 4th. The 200+ men who where gathering around the Tol Plantation were surprised by the Japanese on the morning of the 3rd. Some escaped into the surrounding jungle, but about 170 were captured. The next day, the Japanese began taking the men into the jungle in small groups to execute them. Private Cook of the 2/10 Field Ambulance unit is just one of a few stories of survivors from this event.
The news of the event reached the commander on the island, Colonel John Scanlan causing him to decide to surrender rather than risk another incident like the one at Tol.