The white powdery stuff on the outside of the pot definitely looks like 'efflorescence' that you see on red bricks, which like your pot, are also made out of clay.
When bricks (or other things made out of clay and baked in a kiln - like your clay pot) get wet, the salt inside dissolves and leaches through to the surface. The surface of the bricks turn white when this water evaporates, leaving salt deposits on the brick face. This process is known as efflorescence.
https://etbricks.co.uk/brick-articles/efflorescence-on-bricks-the-causes-prevention-and-cure/
If the salts have leached to the outside of the pot, I'm absolutely certain some will have leached into the wine on the inside! You won't see it on the inside of the pot because the salts will be dissolved in solution with the wine on the inside. Salts are not something you really want in your wine at all, are they? Probably won't taste very nice (hmmm... salty), and may even be harmful to health if the salts are present in the wine in high enough concentrations, which they may well be.
!!!!!!!!!! DUMP IT !!!!!!!!!! <<-- My strong recommendation
Next time you try to make wine, use a glass, plastic (food grade), or stainless-steel fermenting vessel, because they work well, are easy to clean and sterilise, easy to fit an airlock to, and they don't add unwanted salty chemicals to your wines. You might have gotten away a clay pot if it was glazed, but yours isn't, and why bother with a clay pot when modern alternatives work much better than what they had in Ancient Rome or Greece, and are even quite affordable.