Obviously a fine soldier. I understand most of it but what happened in New Guinea?
I don't know what specifically he got it for - it was awarded quite commonly - for 30 days service in Papua New Guinea in nation building, training and administration of defence forces, and humanitarian relief from 3 September 1945 to 16 September 1975.
During that period, PNG was part of Australia, so there were ample opportunities for Australian servicemen to serve there. Given his experience, my guess is he was probably training local troops.