Apparently swans are. I’d guess most birds, especially geese, since their feathers make nice pillows.
https://en.wikipedia.org/wiki/Black_swan_theory
"Taleb's "black swan theory" refers only to unexpected events of large magnitude and consequence and their dominant role in history. Such events, considered extreme outliers, collectively play vastly larger roles than regular occurrences.[2]:xxi"
This discovery (unexpected behavior of matter) seems like it'll have a surprising and large magnitude.
It just means something very rare, and that's been the common meaning of the phrase in English for hundreds of years. It comes from Latin.