That’s normal. On BIOS systems the stage 1 bootloader (which is what this command installs) is always i386, see https://wiki.archlinux.org/title/GRUB#Installation_2 .
What surprises me is that the installer runs in BIOS mode, because your system should be recent enough to use EFI. When you boot into the installer, you should make sure to select the boot entry that has EFI in its name. That might be the problem, but without seeing the output of grub-install, it’s hard to tell.
Just submitted, I hope my answers are useful for your research