Hi and welcome to the forum.
As others have said... nothing to do with the car's on board charger or the EVSE charging lead (which would protect the car from any damage anyway).
I've had this happen on my own 2012 IMIEV in the UK, also running on 230-240V domestic. As has been said, if you draw too much current from a power outlet in the wall for extended periods, and 3Kw for several hours is a lot for typical domestic wiring (especially if it's on a spur, rather than a ring main - hopefully the language complies here), then that can quite easily happen.
It happened to me when I had no option but to charge from fairly long extension lead, and it melted the Mitsubishi supplied 3 pin British plug to the RCD protector, which tripped the circuit - but funnily enough, neither the RCD on the plug, nor the fuse in the plug went - it was the main breaker in the electrical box in the house. It was a hot day by UK standards (about 32 degrees last year).
The fix was just to remove the melted plug and replace it, and it's all working fine now (though I replaced it with a hard plastic one, rather than the soppy soft-touch rubber-type Mitsubishi had supplied - so get a good quality one).
I don't tend to use the Mitsubishi supplied charging cable, but rather my Level 2 wall charger and Type2-Type 1 lead,. Even though the charging rate is 3.3-3.6Kw vs 3 from the standard kit, the wall charger is wired directly to my home fuse box via a short cable with a 6 or 8mm cross sectional diameter, rather than 2.5mm from standard wall outlets - so it's far safer, and offers far lower resistance - better all round... never had any issues.
If you were really unlucky with a wall outlet melt, then I could envisage it damaging the wiring in the wall, which could be a significant pain, and potentially highly costly to fix... which is another reason I try not to charge off a standard domestic plug, especially if I need a full charge, and any length of extension lead.
Looks like you have found a nice low-mileage car, which should be fine, but do get the battery health checked out, as very hot weather and prolonged full charge state isn't good for the battery... and change the 12v battery as a precaution, unless you can verify it has been changed fairly recently.
2012 I-MIEV Keiko Silver 21K
2010 Insight ES-T 64K
2009 RX400h 4WD - 86K
2001 Accord Type-V (F23 manual)
2009 Hornet CB600F