Earlier quoted context omitted.
The EFI partition is on disk, not in firmware.
Clearly there's some component of UEFI that's in firmware, right? I don't really know all the terminology and such here, so please correct my understanding, but -- even if you don't have a disk, you'll get some UEFI bootloader. I seem to recall that some devices like many Chromebooks will have some extensive EFI blobs in firmware partitions, at least some of which is a read-only "get back to factory settings if you r…
The Chromebook’s user partition is read-write, and the system is read only (save for updates). The “powerwash” factory reset just wipes the user partition. The OS restore (if you can call it that) is not stored in boot flash, just standard data/nvme disk.
If you wipe the whole disk, you still need to use a bootable restore USB to restore it.
This has nothing to do with the fact that it is UEFI booting.