FreeBSD is not a distro. It's not even Linux; it's a completely different kernel and operating system that traces back to even before Linux. It's honestly closer to Darwin than it is to Linux; macOS is technically a BSD. (Not FreeBSD though.)
While you’re correct that FreeBSD is not a Linux distribution, the word “distro” is literally short for distribution. It doesn’t have a different meaning like smart and smartass, it’s more like repo and repository.