You're still misunderstanding me. What I'm saying is that if I had been confronted with the situation I described, a supernatural explanation is not the assumption I'd start with. However, since I'm the one coming up with the hypothesis, I can posit any initial facts I like, and the initial fact I'm positing is that the cause of the phenomenon I'm describing is indeed what would be termed supernatural. It's not a "conclusion" I've reached; it's merely the initial conditions set out in the scenario.
So given those initial conditions (which the scientists conducting the investigation wouldn't be aware of at the beginning), would the scientists be capable of figuring it out? That is, would they be able to determine that it wasn't, or in all likelihood wasn't, the result of a non-"supernatural" cause?
Not unless they fully understood every aspect of how it formed and worked. Otherwise I don't see how they could be certain that a natural explaination won't turn up tommorow.
For example long ago the prospect of a rainbow or thunder storm having a natural explaination would have been ridiculous. There was just no fathomable natural explaination for those things. Yet that was clearly not a good reason to assume a lack of natural cause.
Same answer as before. Yes, by first examining all possible physical explanations and ruling them out. Once that is accomplished (if ever), the supernatural explanation remains. But not before, and not as a starting point.