Well.. I had a closer look at that outlet and it is or shall I say WAS rated al/cu. as for what happened I don't really know! When I got there the maintanance guy had the 60A main to the unit open. I did look in the panel inside the unit and found the breaker for the stove in the open position. It is an FPE and well they do trip right to the "off" position ( And yes I know what everyone here is thinking.. FPE didnt trip!)..
The maintenance guy and the tenant said they didn't touch the breaker for the stove so I have to assume it did trip...
The only thing I could assume happened is over time the connection got loose, and got hot, and this got worse to the point where the wires and the receptacle started to char and possibly got to the point where the charred remains started to actually "track" and BECOME a fault with enough resistance to limit current to a level that would not trip the breaker BUT would generate a heck of a lot of heat, until something did short out and trip a breaker..
This is a shot in the dark but if the original problem was a dead short in that box , I do not think there would be that kind of damage even if the 40A FPE in the panel did not trip because the 60A in the panel in the hall and no more than 40 feet away would soon trip.. If it were to fail to trip also, I would hope the 400A fuses for the floor would eventually open but not without damage to the apartment and stove conductors... No damage to those conductors was found other than what was near the " hot spot" and like I mentioned the 40A appeared tripped.
What gets me is the tenant did not notice a problem or smell anything burning until the stove quit and he SAW sparks behind the stove and heard a bang!