I do doubt that he made it "secret" though specifically to make it more headline grabbing. I expect he made it closed so it woudln't be public disclosure and wouldn't prevent him from patenting stuff. IIRC, he's peripherally involved in the CRISPR patent that will likely generate billions. The technology reported here undoubtedly has a giant amount of potential if patented as well.
I have also heard statements that they made it closed so when published it would get into better journals and be more novel. I'm skeptical about this, as the top journals are still going to gobble it up, and also Church could practically record himself farting and it would be considered for "Science."