Is it mold at the bottom of my pot or is it just the metal of the pot just reacting to the cooking process?

I cooked a stew a few days ago and some chopped onions got burnt and stuck to the bottom of the pot during the cooking process. When we finished the stew, there was like some burnt onions at the bottom of the pot, so I just put it in the sink. My girlfriend then washed the pot up. But today I found there to be... show more I cooked a stew a few days ago and some chopped onions got burnt and stuck to the bottom of the pot during the cooking process.

When we finished the stew, there was like some burnt onions at the bottom of the pot, so I just put it in the sink.

My girlfriend then washed the pot up. But today I found there to be like white spot marks at the base of the pot. Initially I thought that it might be mold due to her not cleaning the pot throroughly enough when washing the burnt bits at the base of the pot.

But she says she thinks it's just white spot marks that have appeared because the pot has been used a lot.

I have just boiled some water in the pot and the white spots are still there. I tried rubbing them as well but they are still there.

Could they just be stains on the base of the pot due to overuse or could it be that they are spots of white mold?
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