I do see what looks to be a cord going across the grates, and yes looks like some sort of metal melted, so I would say a heating devise that was apart of the container or this was placed on a heating devise (electric) to warm the container slowly but got too hot?
It looks like one of those european electric coffee pots that you fill with water and plug in. And it further looks like maybe it stopped working so someone thought, "Hey, I bet I can just put it on the gas stove to make my coffee."
A bunsen burner with yellow flame burns at ~1800 F
Natural Gas ~3,614 F
Propane ~3254 F
Mike, as you point out the MP of AL is around 1220 F so if it was (most likely) a thin aluminum bottom, the gas stove is more than hot enough to melt the bottom.
CptBzy: Without specific witness statement(s)and further review of the unburn't portion of the room and counter,(to rule out other sources) I cannot answer your thread accurately. Could be accidental; could be children, could be an elderly subject with early stage alzheimers; could have been left on a gas burner (with pilot on all the time) causing slow pyrolysis the decanter over time, could have thought it was ok to heat that decanter, or could have even been a cover up for potential arson intent. So from just a single photo and not all the facts:
Cause: Plastic Decanter placed too close to a Heating Source.
Determination: (Undetermined) due to lack of interview(s) to determine if the evidence found at the scene matches any/all witness statements to conclude a factual finding.
I have seen a gas (pressure) problem at a plant, for which made pilots look like blow torches in peoples homes...