I think it qualifies as a black swan even if Voldemort set it up. Black swans are just extremely rare, hard to predict events with huge consequences.
(Missing grandparent was mine; I deleted it when I read further in the thread and discovered that Yvain had already made my point, and done a better job than I had.)
If what actually happened was that Voldemort cast the killing curse and it bounced, then yes, that'd be a black swan. But I think it's more likely that he didn't cast the killing curse on Harry at all - he just set it up to look like he did and then went underground, as part of some larger plan. If that counts as a black swan, many complicated plots would too, and I'm pretty sure I've never seen the term used that way.
ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
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