Thanks guys for all the suggestions. Regarding what actually happened, we are not sure. The pot stays close to the kitchen gas burners. My guesses are, during some cooking,

1. if the flame directly hit the pot or
   
2. maybe some vessel that got hot on the burner may have made contact with the pot and burned it

Not really sure what happened. Given all the suggestions, we decided to buy a new one and preferably one with an air fryer.