It doesn't matter if MacOS is advertised as UNIX or not. Technically, it is UNIX. The practical issue is that you are using GNU programs written with the Linux

It doesn't matter if MacOS is advertised as UNIX or not. Technically, it is UNIX. The practical issue is that you are using GNU programs written with the Linux/GNU operating system in mind. Of course this experience is sub-par on the Mac, because neither the Octave- nor the Gnuplot-developers see Mac OS X as their primary market.