Mac OS 'from the ground up' is, actually, Unix, with a layer of sweet, sticky Apple stuff on top
"Security is built into the Mac OS from the ground up".
Correction: the only thing 'built into Mac OS *from the ground up*', is the flavour of Unix that *is* the Mac operating system, and that, sure as me2Phones are me2Phones, wasn't built by Apple. It was 'borrowed', in the best Apple traditions, as heJobs, himself, boasted in the late 90s (about Apple's use of other people's ideas, that is).
The part that Apple added was the shiny, pointy, clicky, swipey stuff, stuck on the top of the OS, which some swoon over and others think is just a little shell-suit-style tacky. This, the GUI, is not at the heart of any security claims. The OS (Unix) is, and credit for that goes right back to the original design at Bell Labs in the 1960s. For that, Linux users tip their hats in gratitude and give due credit, whilst Mac fanbois, albeit usually in ignorance, mostly tend to believe that iJobs actually knew something about software, perhaps even wrote some. Such is the faith of true believers.