Praise then darkness, and creation unfinished

Someone on my friends list described an odd encounter with a stranger. After posting a comment in which I suggested one possible motivation, I found myself wondering (as we used to when people did harmless but attention-getting things in Freshman Commons [a large dining hall] when I was in college) whether the entire thing was a put-on by a psych student, designed to see how she, and other passers-by, would react.

Then I discarded that, on the grounds that while it could in theory be the explanation for almost anything, it's unlikely, unsatisfying (if only to the story-telling mind), and in this case untestable. And then I found myself wondering, what's the null hypothesis? Presumably not that the entire incident never happened, either that my friend is making this up to see how we react, or that she dreamed or otherwise imagined the encounter. Not the psych student--the percentage of interactions on the streets of any city that are put-ons by psych students is statistically insignificant.

I don't think, in the technical sense of the term, that there is a null hypothesis for the general question "Why did that person do that odd thing?" There probably isn't even a most-likely-guess for the question in general, if only because the set of odd behaviors is so broad, as well as so context-dependent.