Stock installer boots via 64-bit EFI

boot.installer-efi64AutomaticHigh confidence

How it tests

Reads the EFI bitness the firmware handed the kernel (fw_platform_size). If OmaBoot? is running and the firmware is 64-bit EFI, the image booted through 64-bit EFI and GRUB.

How it decides

Supported when the firmware is 64-bit EFI. Not tested (other) when the Mac booted in BIOS compatibility mode.

How sure it is

If OmaBoot? runs, the image booted. It's one step removed from the stock installer it stands for: same kernel and packages, but our own boot menu, boot options and a smaller image.

What could mislead it

Could pass when it shouldn'tThe tester picked “safe graphics” (nomodeset) or another non-default entry, which the stock ISO's default entry doesn't use. The evidence names the kernel, not the entry.
Could pass when it shouldn'tA difference between our image and the stock ISO (GRUB theme, kernel options such as the radeon panel fix, image size and USB load time) lets ours boot where the stock one hangs.