Interesting comments Dr. and quite relevant I believe. Due to a spur of the moment decision on the day for work I flew the near exact same route (Tyabb - Mel - YSHT) earlier that day in a VFR single. My flight level was 9,500ft from YMML to YSHT and the weather (and ride) couldn't have been more perfect aside from the wind. The reciprocal return leg was only several hours prior to the incident, but the ride could not have been smoother. I was fully aware of the forecast and was expecting some grief so when I heard the news of a breakup I was blown away considering the weather that I experienced earlier. In my opinion it was literally a case of had they been a couple of thousand higher they would not have had an issue. It really was a case in my mind of "only if they had..." for them.
I've had some pretty average weather just north of Melbourne in my time, particularly down low (up to 5-6k ft) The areas south-south west of the Macedon ranges can give you 40-50 knots in a northerly when nothing significant is forecast and often result in a sigmet.