Your observation is correct. Raspberry Pi does not use GRUB at all.
GRUB is not universal in the Linux world, but a bootloader for some specific hardware architectures:
- 32- and 64-bit x86 PCs, using BIOS, UEFI or Coreboot firmware
- SPARC systems
- MIPS Lemote Yeeloong systems
- certain Qemu emulation environments.
Raspberry Pi is an ARM device, which is none of the above. It has its own firmware and bootloader.
The first stage bootloader is stored in ROM within the RasPi's system-on-chip.
bootcode.bin from the SD card. That will load
start.elf, which will then load
kernel.img. In older versions of RasPi firmware, there used to be
loader.bin step in between
config.txt settings: http://rpf.io/configtxtreadme
cmdline.txt is the place for the Linux kernel boot options.