Desert Flower has made one of the few rational posts here. And if you look at the BOM observations at MtGambier today you can pretty much see it. It looks like Fog either formed, or maybe reformed after clearing at about 10:30, then cleared again by 11.
And as for jobsright, or is it jobsworth the AF I that you refer to as Nhil which actually crashed 30km North of Horsham has very little in common with this accident. Drawing a parallel between the 2 is either malicious or plain ignorant.
This is a sad accident. I do not know the pilot and I.m not sure that any of the posters so far do. I don't know if he had a commercial licence or private licence nor if he was VFR or IFR and jumping to conclusions based on predjudice does no one any favours - least of all the image of those posting.
I take on face value the media reports that he was an experienced pilot who flew to MtGambier regularly. He had flown from Adelaide that morning, so should have been familiar with the enroute weather.