Reading the original post again, I am a bit confused. The aircraft was basically tracking SE in the Dimboola area, so I would guess it was an Adelaide-Melbourne Flight, then you said it was seen going NW(?????) and that made you think it was going to Sydney(????), NW would take it to Alice Springs. I stick to my original theory and that being it was originally tracking AD-ML and then was given a dogleg or 2 to lose some time for sequencing. But I reckon we should get the tapes pulled and find out the reason why.
