Apple's EFI firmware has an HFS driver built into it. The way today's macOS boots is the firmware reads the bootloader off the boot partition created these days

Apple's EFI firmware has an HFS driver built into it. The way today's macOS boots is the firmware reads the bootloader off the boot partition created these days on Core Storage installations, and the bootloader (more correctly OSLoader) is what enables the firmware pre-boot environment to read core storage (encrypted or not) and thus find and load the kernel and kext cache and then boot.