Why does driver's seat move on its own?

Some kind of memory setting

Yes. The memory seat position set button is in the driver's door panel, and it's wiring goes through the boot between the door and the car body. Each time you move the door, those wires in the boot bend, and over time they can break. In your case, this has caused an electrical short that runs each time you open the door. It's a simple fix; just repair the wire break. But getting to it and finding it is something else.

It’s called easy exit/entry mode. It is programmed into the menu items in the dash display. More information can be found in the owners manual, please read it.