They probably changed the name before it's no longer PowerPC dependent.
I mean why not call it ARMBoot?
It should not be called ARMBoot, because:
1: The original name of the project was 8xxROM - not ARMBoot.
2: ARMBoot was made on basis of it's sister project (PPCBoot).
3: The AmigaOne PPCBoot was made on basis of PPCBoot 1.1.6, and not ARMBoot!
4: ARMBoot is no longer ARMBoot, but has merged with PPCBoot to U-Boot.