The criminals feel that it's not enough to just plant the trees, they have to be ones likely to survive the future, considering local climate and possible government employee interference.
The criminal was seen with his accomplice planting eucalypts and paperbarks, and an olive tree. Fruit trees were not favoured at the time because those require a temperate climate with decent rainfall, and at the time it was fucking hot (110F) and had not rained for eight weeks, so it was felt that oranges, peaches, apples and the like would be unlikely to survive. Natives and trees bred to hot dry climates seemed to have a better chance of establishing themselves.
Also, because council and state policy is rather enamoured of concreting everything, if any plants are found some place they're not meant to be - like where criminals planted them - they may get tipped over by interfering government employees. State and council policy is at the same time overprotective of native species, so if they're native they've a better chance of not being pulled up. Whereas most fruit trees, they'll be able to use, "oh but what if an apple fell on a member of the public's head?! What if someone ate the fruit and got a squirty bottom?! Oh noes!" as an excuse to tip it over.