In my opinion (emphasis opinion), "black swan" includes the concept of
timing... that a pandemic would occur is inevitable, but you have no idea on the timing. Market crashes are inevitable, but you have no idea on the timing. Volcanic eruptions are inevitable, but you have no idea on the timing. etc.
Things that are inevitable only when you encompass time spans longer than a human life (it has been approximately one and a half average human lifespans since the previous pandemic) may be predictable at that large aggregate scale, but on useful scales they are not. Or, to put it another way, if you've been shorting the market since 1918 for the next pandemic crash, you went bankrupt a long time ago.
Y2K is only a black swan for those not in the industry, since that one is obviously intrinsically timing based. The UNIX timestamp equivalent is also equally predictable to you and I, but to the rest of the world will seem even more arbitrary if it's still a problem by then. (At least Y2K was visibly obviously special on the normal human calendar.) But I wouldn't claim the term for that; call it a bit of sloppiness in my writing.