It makes sense that with water in the pot you are safe with flimsier materials. I guess where there is water, the pot can only be a little hotter than the boiling point. If it was empty I suppose the pot would just approach the heat of the flame, which, using the magic of the internet, can ran from 300*C to 600*C at the flame tip to between 900*C and 1200*C at the continuous flame region.
Meanwhile the melting point for Al is 660.32*C. Definite problems with an empty pot. In contrast, Ti has a melting point of 1668*C. No problem there!