I have great respect for Haynie, but in this case I think he's just conjecturing. He has no proof that the MOS sources are stolen from AmigaOS and never will have. And such a claim doesn't even make sense considering
1) The limited usefulness of the AOS sources;
2) The fact that MOS was begun with AROS sources, which are certainly not stolen;
3) MOS (or rather QBox) is very different structurally than AOS. It has AOS emulation using native code, called ABox. No more, no less.