There are many ways to install third-party software. Some are harder: download source and build from it yourself (while handling any cross-platform issues, etc). Some are easier: just install from an OS supplied package. The latter still works for GCC on FreeBSD.
I'd argue that the software provided via the ports is not part of the OS. But the FreeBSD ports themselves (and official packages built from them) can be considered part of FreeBSD.
P.S.
You can disagree with me and state your point, but you do not have to downvote me.
