What Fallacy involves asking a question with an unrelated presumption

It is possible that it was filmed on a stage. That's not evidence. That's just a possibility.

It's also possible that our brains are inside vats. That's also not evidence that they are definitely inside vats, it's just a possibility.

appeal to possibility

This is a burden of proof matter.

When people are in a discussion, and one presents a proposition, unless it is one already agreed upon, the propounder carries the burden of proof to substantiate the proposition. This rule of logic has been around since Aristotle, or maybe Thales. 

I think it is obvious that unless one has evidence to believe something, there is no basis upon which to believe it. Hitchens’s razor puts it, “what may be asserted without evidence, may be dismissed without evidence.” Carl Sagan added what has become the Sagan standard: “extraordinary claims require extraordinary evidence.”

So, when someone presents a proposition but no evidence, the proper response is not to believe it, point out the lack of evidence for the proposition, and ask the propounder to provide some evidence.

If evidence is forthcoming, then the burden of proof shifts to you. You can accept the evidence or, if you do not find the evidence convincing, it is your burden to explain why.