Well, I'm using a BSD system right now (that 'feline' one). Too bad it's got something messed up, hopefully it will get better with the latest version.
I think you are implying that OSX is a BSD. Just because you have some BSD userland utilities doesn't make you a BSD. OSX has a totally different kernel than any BSD (mach).
The Mach micro-kernel was originally a BSD kernel fork (iirc 4.2BSD, when dinosaurs roamed the earth). NeXT/Apple added various things like DriverKit and later IOKit to Mach. Apple also took the network stack from FreeBSD, which is traditionally rather modular (for high performance kernel code, anyway).
Together they make up the current XNU hybrid kernel. You can look at most of the sources at opensource.apple.com
There's certainly lots of FreeBSD in OSX, but it's not like OSX is just FreeBSD with a sugar coated Apple UI.