It was never said he was satisfied with the outcome. In fact, he even said there were still a lot they didn't get. However, they got the worst of it. They also exposed a large network of what was happening, including releasing the tape. So, the cult can't hide in the shadows. 'Once, it was all darkness. Now, there is some light.' They weren't just talking about the stars. It was a metaphor for the case itself. Rust also is not optimistic, as he was the reason the light appeared.
By satisfied I meant "accepting." They actually didn't expose the network because the news said that Tuttle's connection to it had been dismissed. So they failed in that regard. With how obsessed Rust was with the Tuttles, I can't see how he could possibly think that the "light is winning."