It seams to be a problem in between legacy and EFI boot. Have a look to this article in Arch linux:
[SOLVED] Grub error: file '/boot/grub/i386-pc/normal.mod' not found / Newbie Corner / Arch Linux Forums
The “i386-pc” in the error indicates that a non-UEFI version of GRUB is attempting to boot. Is UEFI mode enabled and non-UEFI (CSM or “Legacy”) mode disabled in the firmware (“BIOS”) options?
Are you sure the Arch ISO was booted in UEFI mode when you ran those commands? How did you check? Were there any error messages after running them?