Amiga OS 4.1 is a redesign of the Amiga OS that includes a core kernel that directly supports the PPC processor; it is uses Unix-like structures but is NOT Unix/Linux. On Classic Amiga's the operating system is purely Amiga. There are changes that made for a modern OS and compromises made for efficientcy sake.
It, as was the original Amiga OS, bases itself on a preemptive multi-taking core as does U/Linux. There are no courses in Amiga programming taught in college (at University). So that leaves Windows and the *nix's as multitasking systems being taught today. Folks follow programming principles in programming OS 4; you will find a great deal of older programs run on OS 4 on Classic Amiga's as do newer programs. What is now amazing is that you can throw a PPC processor into a motherboard and OS 4 will run on it. I just love it running on my A4000T