If he was flaunting it in everyone's face and not allowing anyone to ever play it - that would be one thing. As for private mods, there are many of them that no one ever gets because the creator chooses not to release them. Reasons could be anything like abuse, small and not really useful, and so on.
He doesn't have to release it, and he probably shouldn't release it. The last time CityRP/G was given out, practically every server became one. It not only killed the fun of the mod, but it killed most of the fun servers.