This sighting, if it proves relevant, would be consistent with theories suggesting the Malaysian Airlines 777-200 SR was commandeered and re-routed to some remote location, into the variable "heart of darkness" but well inside the realm of the very nasty AQ franchise headquartered in the southern Philippines.
On the map above this sighting would have been near the far northern coast of Sulawesi, or, if you prefer, the southern side of the Celebes Sea, at about 120° plus - southeast of the "last contact, rather than the 90° course indicated. About two hours flight time, more at low altitude, but still well before pre-dawn twilight.
I would not, definitely not, give the AQ Philippians credit for such an operation, but they might serve well as actors providing a hypothetical staging area for a cooperative operation whose end-game would still be unknown, one that perhaps included Tehran and God knows who else.
That group likes hostages, too.
They had the fuel, perhaps the skill.
If one were inclined to speculate further, and imagine such an hypothetical operation still underway, a wider search concentrated under the last contact would allow time to prepare for using the aircraft as a weapon, while attention in concentrated elsewhere.
However, such hypothetical conspirators would still need to act quickly because they will not be able to hide indefinitely.
The time of this Red Eye flight would have granted sufficient cover before local sunrise, the fuel was heavy, and perhaps most ominously, the aircraft has an very long range.
The Australians and perhaps the Japanese should exercise due diligence. .