You don't really read, do you? MacOS isn't UNIX. It isn't UNIX any more than BSD is UNIX. BSD is not UNIX either. It's UNIX derived. BSD forked off of UNIX a long time ago, so they're not one and the same. UNIX still exists separately from BSD. Every carefully worded and accurate article makes sure to point out that MacOS X is UNIX-based... not UNIX. (refer to the articles I cited above and also http://en.wikipedia.org/wiki/Mac_OS_X)

I will concede on one point of miswording on my part, though. MacOS is actually running the XNU kernel. Period. The SNU kernel is MAINLY based on BSD and based in PART on portions of Mach--so we're both right, actually. It's a BSD and Mach kernel mishmash.. so it isn't really a distro for BSD so much as a distro (collection of kernel with commands and applications for a complete and usable operating system) for XNU.