Well, obviously nobody has looked at it all that closely, so I'll say why I find it interesting.
It's an engine shutdown. That's pretty much shown by the intermediate altitude chosen after the turn. I will admit that I knew that from other sources.
A twin with an engine shut down is in an emergency situation. You really should land at the first available airfield. There are a couple of provisos to that, but they are not commercial ones. Curfews also can be disregarded. Melbourne should not be the first choice. Third perhaps.
The wind on the night in the area was roughly westerly at 50 knots or so. That fits in reasonably with the ground speed shown before the turn (424 knots), and gives a cruising IAS of about 260 knots, and mach .82....which would be about right.
The descent is started at 1349 (perhaps a few seconds earlier). Prior to that, from 1344 to 1348 (and a bit) the aircraft has maintained height, but has turned from a track of 307º to 284º. Not a big turn, and it would not dramatically affect the ground speed (perhaps 10 knots). But, the speed has decayed from that initial 424 knots, back to 344 knots. So, I'd expect a g/s of 414, but we're actually 70 knots below that. So, that means that the IAS/mach has reduced. Now, given that you've shut an engine down at altitude, and the aircraft is not capable of maintaining that height on one engine, that isn't unexpected, but how much speed has actually disappeared? Playing with the calculator a bit more, I get a TAS of 390 knots, which converts to a mach of .67, and IAS of about 212 knots. That is very slow.
It will be interesting to see if the ATSB look at it at all, and if so, what they make of it.