You said that your new to casting, is your pot new? If it is I would be on the phone to who-ever made it and trying to get free parts shipped to me under warranty.
You did absolutely nothing wrong and the cold air had nothing to do with it. Heating elements are resistive loads and can only draw what they are rated for unless they ground out.
What brand and model is the pot?
If the heating element grounded out and didn't weld itself solid to the metal around it, you wont' see a ground on your meter because it grounded when it was hot and stretched out. Now it's cold
They usually burn off though.
If it's rated for 750 watts than, it can only draw 750 watts to heat in any condition. It like an incandescent light bulb. They're plugged into 15 amp circuits but can only pull the rated wattage or they would burn out immediately when turned on.
It blew your breaker so the something inside grounded out and maybe burned off.
Check your switch also for grounds, it should just be a simple thermostatic switch that is on or off, nothing in between.
If your switch is cooked you already know what is wrong.