This is a wrong use of the term.

Black swans are rare but actually exist.

https://en.wikipedia.org/wiki/Black_swan_theory

It's actually a correct use of the term. A “black swan” is something that is believed not to be possible – or, in retrospect, something that was believed impossible but happened anyway.

The term predates the discovery of black swans;

> However, in 1697, Dutch explorers led by Willem de Vlamingh became the first Europeans to see black swans, in Western Australia.[9] The term subsequently metamorphosed to connote the idea that a perceived impossibility might later be disproven. Taleb notes that in the 19th century, John Stuart Mill used the black swan logical fallacy as a new term to identify falsification.[10]