"This foundation is a core operating system commonly known as Darwin. Darwin integrates a number of technologies, most importantly Mach 3.0, operating-system services based on 4.4BSD (Berkeley Software Distribution)"
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The operative words there are *based on*. Mach is driven by a microkernel whereas BSD's core is monolithic.
They are very different in that respect.
Apple's implementation is a hybrid. They don't use the BSD kernel, only the rest of BSD to handle the higher-level stuff, passing everything to the Mach kernel for low-level handling. But in this case Mach is compiled into BSD instead of being standalone with message passing between them.