For those that are into what I would call "deep conspiracy", the significance of this whole TMFINR incident should not be underestimated. "Deep conspiracy" is where you're actually trying to figure out just what the hell is going on in the world, rather than (1) reacting to the flow of news, or (2) digging up all the evidence that proves you were right all along.

TPTB are going to excessive lengths to cover up whatever seems to have spilled over in the back of that plane. People who wonder what goes on in the strangest, darkest corners of the world typically just make it up according to their preferences and prejudices rather than looking for and studying the transient anomalies such as this one. Too much work, I suppose.

What did Airplane Lady (is her name even Tiffany?) really see that caused her to flip out? Filling in the context, I'd say it was a person sitting next to her that she--being the outgoing sort--was interacting with until it slowly dawned on her that that person... was something other than a person.

The touchstone here is the "Men in Black" phenomenon. They're said to often have a strange appearance, like plastic-looking skin or an ill-fitting wig, but what really puts people off is their behavior.

We've all interacted with innumerable people over the course of our lives--and seen and read about many others--and we are incredibly attuned to the entire range of normal and even abnormal human behavior. Anything outside of that range is deeply disturbing and literally unnatural.

So best guess? A soulless humanoid, a biological robot, useful for certain kinds of tasks. Maybe TPTB were just field testing and this one failed. Who knows how many did not?