[krisoft]

> They ruled out--according to this source--a hypothesis based on where the light was.

That is your reading of the sentence. "choose to assume" does not mean that they ruled out other options. It especially does not mean that they ruled out other options when it is combined with the second part of the sentence which describe that the reason they took this assumption is due to resource constraints.

> Have you flown a plane?

Yes.

> This isn't a "who knows" situation.

You are misunderstanding the whole paragraph. The "who knows" situation is what you, JumpCrisscross was thinking when you wrote "What in the actual fuck.". If instead of emotional venting you would have wrote a complete and full sentence we would not have had to speculate what you are incredulous about. Clear?