There seems to be quite a disconnect between the ATSB's summary (and what is subsequently reported to the press), and the "contributing safety factors" within the report.
Summary
The aircraft was not in the correct landing configuration by 500 ft height above the aerodrome and, as required by the operator's procedures in the case of an unstable approach, the crew carried out a missed approach.
Report
The flight crew continued the approach despite not being able to satisfy the operator’s stabilised approach criteria prior to the stipulated 500 ft in visual meteorological conditions.
...commencement of the go-around, at 392 ft. Both crew stated that they were unaware of the minimum height reached before the aircraft climbed, but believed that they initiated the go-around just below 800 ft RADALT.
The summary and reporting in the press seems to suggest that they had sufficient situational awareness to realise that the approach was unstable and had anticipated the go around. It would seem to me that the trigger to initiate the missed approach was the GPWS warning.