I did a little investigating and the only thing I came up with is to remove build up of cooked on stuff. It says to do it over medium flame, which would be a gas stove, I'm thinking, but the same would happen over an outdoor fire. It turns the build up to ash and makes it easy to clean.
That's basically what my self cleaning oven does. It gets up to about 700 degrees and turns burnt on stuff to ash so it can just be wiped out once it cools.
Makes sense to me. She must have been cleaning it.

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