There are still lots of other confounding variables there that you need to factor into the probability.

Maybe I shouldn't say overwhelmingly likely for all of those possibilities - a lab escape isn't that unlikely. But there's no evidence of that. If it's true, we indeed may never discover any evidence, but evidence is still required to actually make the claim. As it is now, it's only worthy of speculation.

edit: I edited my original post to make my beliefs more clear.