I’m using hypothesis informally. “God exists” is a hypothesis, as is “God created the universe”, for example. That’s the feeling I got from the brief quote. I haven’t read anything by Carroll beyond that, so I won’t say more!
How likely is a God that could create all those things?
Why restrict this to “God”? That’s just one possible supernatural entity among many. It doesn’t make much sense to say “the natural is anything but the supernatural” however. I might say “whatever exists in reality”.