Although, given the 1918 Flupandemic and several other historical precedents, it should not have been a black swan, since it was known to occur. I've heard these referred to as "gray swans"; i.e. things that have the same impact as black swans but even prior to the fact there were people who were predicting it.
For example, the David Quammen book "Spillover" essentially predicts it, and it was published in 2013 (subtitle: "Animal Infections and the Next Human Pandemic").
I do think this is appropriate though since a key characteristic of a black swan is that people can look right at it but not see it due to psychological biases.
Agreed, but "black swan to most people but white swan to a few" is harder to say than "gray swan".
For that matter, Nassim Taleb himself predicted that the American mortgage industry was, I think he wrote something like "a barrel of dynamite" or some words to that affect. But, for most people, the mortgage crisis was a black swan.
The original metaphor, though, was that no matter how many swans you looked at in Europe, and how carefully, you would have zero data to tell you that black swans were possible, until you went to another country and discovered them.
For example, the David Quammen book "Spillover" essentially predicts it, and it was published in 2013 (subtitle: "Animal Infections and the Next Human Pandemic").