Rbl charts, page-214

They may have not bought them all back. It may just be a reporting omission. Check out the ASIC short reporting page for the caveate.

"It is important to note that ASIC’s aggregated short position reports are reliant on the accuracy of reports we receive from individual short sellers. While we will monitor compliance with short position reporting and provide additional guidance where necessary, we are unable to verify the accuracy of all individual reports submitted to ASIC, nor to verify that all short sellers in our market (both in Australia and overseas) are lodging reports.

Disclaimer: No responsibility is accepted for any inaccuracies contained in the matter published."