I'll put it in basic terms, it's not 100% accurate this way, but it makes the message more clear (I think)
OSX is based on a Unix kernel
BSD is basically a Unix kernel
The Linux kernel is unix-like, but it is, in reality, quite different
Hope that makes sense.
I'd like to make clear (again) that I know that's a very big over-simplification, but it should hopefully point out the difference a bit better
