I guess you have to think of the buyback in terms of the amount...

I guess you have to think of the buyback in terms of the amount of shares held by the Kongs. Given that their listed holdings add up to more than the total shares issued, I assume there is an overlap of ownership, so taking the larger holding of 855,664,357 shares, that only leaves 436,071,283 shares on the open market, which means they are buying back about 4% of available shares (given that I presume they have no intention of selling any!)

NB The owners shareholding is from last AR so doesnt include any shares from the DRP.