This is true, but the differences go even further than that. Redox is intentionally non-posix-compliant. This means that userspace programs written for posix operating systems may or may not need patching to even compile.
Part of the philosophy of Redox is to follow the beaten path mostly, but not be afraid of exploring better ideas when appropriate.
I'm not sure. I remember seeing an example in the docs, but I can't find it now. Actually the docs in general are a lot less opinionated than I remember them.
One thing that I did find is that the ion shell document mentions that it isn't a posix compliant shell because they would have had to leave out a bunch of features.