Hello,
It's plain to see that Amiga code was used.
They can say that they didn't use it if they wish, but I know better than that.
Well, let's check that. Have you ever developped APIs compatible with other OS APIs using just public documentation? Considering what you said, I doubt a lot you've ever tried.
To give a concrete example which is outside our Amiga world, that's what the OpenBeOS Team is actually doing to be compatible with BeOS, and guess what, it looks exactly like BeOS! In fact when it'll be finish it'll be very hard to see the difference between OpenBeOS and BeOS. But they just used the public developper documentations (this include the OS public includes, the BeOS Bible...etc) and don't use at all any part of the BeOS code.
If you had just searched a bit over the net OSes API compatible with others you'd see it's totally possible to make an OS that just work like another one without using any original code and just the documentation (OpenBeOS, BlueEyed OS, others BeOS compatible projects, AROS and of course MorphOS).
For me it's obvious that by saying that "It's plain to see that Amiga code was used." show clearly that you have no clue the technical aspect.
You know that's not because MorphOS or AROS looks like AmigaOS that they have used AmigaOS code. Just like OpenBeOS elements which just looks like the real BeOS but have been rewritten without any part of the BeOS code.
In a nutshell, it's not possible to say just by looking at an OS if it has used code of another one. What I know personnaly is that OpenBeOS didn't use any original BeOS code and AFAIK this is also the case of AROS and MorphOS. At least I know it's perfectly possible to make an OS compatible with another without using any part of the original OS code. And I don't see why it'd not be the case for MorphOS and AROS (particularly considering that AmigaOS is extremely well documented and the time of development (AROS has started years ago and MorphOS has been faster because the MOS Team can use the work already done by the AROS Team).
Regards