FreeBSD isn't Linux, Linux isn't Unix, GNU's not Unix...
But they're all Free Software, and that's the main thing.
If you're beginning to learn C, perl, etc. the differences
in distros (and kernel) won't concern you much. Some but
not much, and you'll have to deal with updates within one
distro anyway. Just get a working install, take it from there.
(Make sure gcc, browser & editor you choose work)