Embedded C++ is a C++ subset, it is as valid C++ example as those embedded C dialects that aren't able to fully support the ISO C standard library, yet people still call them C.

And as of Driver Kit introduction, 100% full C++ is now an option.

In a couple of years from now, when the full transition of kernel extensions to user space modules is complete, the kernel will be the only C piece left.

Which Apple most likely won't bother to rewrite due to the historical baggage of mixing BSD with Mach code that probably no one is willing to re-write.