Care to elaborate why? Read up some FPGA systems (like some retrogaming computers reproduced in FPGA) and you can see that the FPGA can load whatever it wants from SD and turn it into whatever it needs to.
The SRAM (there needs to be one) chip stores the save till you reset in DS mode, then the manager dumps the save from the chip, saves it in .sav format, and empties the SRAM chip for the next game.
The physical switch is needed to go from 3DS mode ("1:1") to DS mode, where you get the manager.
It can also get power directly from the 3DS if there's no manager. While it is in the 3DS's system menu, the 3DS gives power to the cartridge. Press the switch, the FPGA dumps the save (it just needs some power to do that). Simples.