It does say "Auto". I'm pretty sure that if it is selected, it runs EFI files, and if it is not selected, it runs legacy MBR.
That said, you probably want GPT to be enabled. See this for more information.
Hmm, in my opinion "auto" runs legacy BIOS if there is no EFI files and configs.
If I remember correctly, I have it set "auto" and it runs non EFI boot.