Unsure if they have checked the KPIs of Metcash (the main supplier) as the "...risk of engaging with a business with a record of modern slavery practices is negligible …" (section 6, pg 4)

the assessment practice would indicate that they require safe guards when suppliers were to be "at risk" (page 4, section 6)

Definitely a judgement call here, but I believe you selected the best option. Since it's not explicitly listed, unknown or no are only right options

Correction, it has to be no