Less laconically, distros generally refer to the userland parts of the operating systems rather than the actual kernel. FreeBSD does not use the Linux kernel so calling it a distro, which typically refer specifically to Linux distros, wouldn't be accurate.
Where are you messing with userland-only options? In my experience a Linux distro not only comes with a kernel, it's almost always a kernel specific to the distro. So I don't understand that reason.
As far as Linux versus not Linux, "distro" feels fine to me for Unix systems.