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Your graphic is incorrect. I think it will help to deconstruct terms as I go along, you have parts of the puzzle correct.
Let's build from what is seen.
Android = Linux (with services) + the Dalvik Virtual Machine (VM) + apps that run in the VM using Linux services
Collectively, that makes up what we colloquially call a ROM. It's not really a ROM, read-only memory, but the name is a holdover from the feature phone days when the os was literally stored on a ROM.
The memory on your phone, aside from ram, is flash memory using nand logic, aka nand flash. Now you know where the terms flashing and nandroid came from.
Your phone storage is divided into quite a few partitions. Varies by model, but 6 or 8 is not uncommon.
The bootloader is somewhat analogous to a PC bios. It is not a bios, but similar in that it's the lowest level executive.
The bootloader contains management functions, chief among them, the vector to the operating system startup and the recovery, critical to installing a ROM update, as happens over the air from time to time.
Linux is a preemptive multitasking operating system, similar to Windows or OS X. The Linux on your phone is true Linux, just like desktop Linux, but tuned and customized for a small memory footprint.
Bootloaders always come locked so curious consumers don't screw with things that they don't understand. Your phone takes that a step further - encryption security is employed so that only critical components with the encrypted key signature can be installed. Your bootloader can't be unlocked because no one has broken the encryption security yet.
The kernel is part of the Linux operating system, and it's what starts first - your encrypted bootloader tracks if it is launching a kernel it knows, even though the kernel is not part of the bootloader.
A nandroid backup contains your Android rom, as defined earlier. Depending on the custom recovery, some folks get the chance to backup Android by its partitions (Android is not in one partition, but several) but most of us use ClockworkMod recovery, and its backups contain all of the Android partitions in one convenient payload. By the way, your app data is stored within one the Linux partitions, so thats why your data and settings are stored with your nandroids.
The SBF is strictly a Motorola construct. It stands for system binary file - it's a full image of your phone system. Other makers have the same sort of thing, but their names and layouts vary as you may expect.
Makes sense?
