Gotcha, I see where you're coming from. I think that the phrase isn't meant to be taken as cold hard logic but a rule of thumb for the default position on a theory. To reiterate, we don't know that any religion is right, but because they contradict each other, we do know that some must be wrong. Since none provide proof, and especially because they all contradict each other, a reasonable person would assume that they're all all wrong until actually finding some evidence.

So yeah, the way it's worded it does sound like a logical expression, but really it's "If 20 people tell you the answer and they all give you different answers without showing their work, it's not safe to bet that any one of them are right"