Or maybe he referred to a black swan event.
It was immediately apparent that it meant a circumstance that wouldn't have been predicted, because no previous experience suggested such a thing was possible.
A quick look around the Net told me that it's a theory proposed by Nassim Taleb. Here's a brief quote from his work, posted on Wikipedia:
What we call here a Black Swan (and capitalize it) is an event with the following three attributes. First, it is an outlier, as it lies outside the realm of regular expectations, because nothing in the past can convincingly point to its possibility. Second, it carries an extreme impact. Third, in spite of its outlier status, human nature makes us concoct explanations for its occurrence after the fact, making it explainable and predictable. I stop and summarize the triplet: rarity, extreme impact, and retrospective (though not prospective) predictability. A small number of Black Swans explains almost everything in our world, from the success of ideas and religions, to the dynamics of historical events, to elements of our own personal lives.
Taleb says there's a 'nice summary' of his ideas at Arlene Goldbard's blog.
She finishes with these points:
Since we can’t control unpredictable events, we should accept uncertainty and seek to maximize our exposure to serendipity, as by putting ourselves in the way of new ideas.
Since there is such danger in accepting conclusions based on too little information simply because they confirm our beliefs, we should try to remain aware in the present of what we are doing, paying attention to what actually happens and refraining as far as possible from imposing theories on our experience.
We should recognize our poor record as a species in predicting the future, that we are much better at doing than knowing. Some things are more predictable than others: we are safe enough in expecting tomorrow’s sunrise to plan on breakfast. We can start noticing which situations are most susceptible to black swans, and when we encounter them, remember how little we truly know so our ignorance doesn’t lead us around by the nose.