O Fallon, MO
That's a floor receptacle. It's a house that was built in the 70's. It was a party / vacation house in an affluent area.
The house is on slab and on a lake. Aluminum wire splices will go bad on their own without help. The moist under-floor environment, coupled with the improper copper spliced in certainly didn't help.
Floor receptacles always seem like a good idea, but they take a beating. Especially in carpet.
If someone refers to herself / himself as a "guru", they probably aren't.