The #1 reason the company implemented the buyback is to support...

The #1 reason the company implemented the buyback is to support the share price in the context of a correcting stock market. All major indices were correcting. Panicky people were pulling money out of risky stocks, retreating to cash or other safer investments.

All Ords dropped from 6301 to to 5993 between 5 October and 11 October a drop of 4.9%. Early signs of a significant correction in play.

As a defensive measure for the share price, in response the company announced the buyback the next day on 12 October.

Two directors had just contributed a combined approx $500k to the placement of as evidenced by the directors interest notices on 20 September, perhaps concerned for their own investments (just a few weeks after putting their significant additional money in) but I'm assuming (and it is implied by the buyback announcement) also generally concerned for the share price and the potential for excessive dilution if the share price drops significantly and they needed to raise further capital.

The Estelle drill campaign was aborted early. They hadn't spent as much money as planned and decided that due to market conditions, a buyback was a measure they could use to help protect the share price.