deadblackclover yes, indeed GhostBSD historically tried to stay truer to its parent project (and generally to Unix simplicity) than TrueOS, even though after GhostBSD's rebasing on the latter, the difference has become extremely subtle.
That said, neither of them is a true fork, which would imply splitting codebase, pursuing different goals and path up until a point where one loses ABI/binary and kernel module compatibility, resulting factually, in 2 different OSes. See GhostBSD and TrueOS respectively as the Antergos and Manjaro counterparts of Arch Linux.
GhostBSD and TrueOS are always in sync with mainstream FreeBSD, they share with it the same codebase, the same exact kernel, and wasn't it for LibreSSL, there would be a 99% likelihood ELF binaries compiled on GhostBSD would work on TrueOS and FreeBSD -CURRENT too. To sum up, both project are FreeBSD, just with a slightly modified userland, and different defaults. Then you see people saying Linux Mint is a Ubuntu fork, fair, it's can be a point of view and a matter of terminology...as long as we all know Linux Mint is Ubuntu.
True OS forks result in divergent development and, in other words, they result in new operating systems; examples of true FreeBSD forks are:
There's a grey area in between which includes project constantly syncing with mainstream, yet locally applying patches critical enough to make them incompatible with the parent project; they are sometimes referred as soft forks; an example is HardenedBSD