Based on the species, I’m assuming this is coastal Southern Australia. That is a pretty mild and excellent climate for trees, so that might have been a factor. In my area (California) you will have much higher mortality if there is no care after planting.

Sounds like he was thoughtful about the specifies and site selection. If you are careful about those things, the trees can get by with less care. The worst projects that see total failure are poor species planted poorly at poor sites with poor care.