Plus there's also the little fact that it was published in the year 2000.
That is as may be, but it is not usual for a work of fiction title to reference where/when it was written. A book title usually conveys to the potential reader what is within.
Yeah, but the millennium wasn't exactly a usual year. And it's perfectly possible for a title to have two or more meanings, including an external meaning as well as one relevant to the story. It's pretty obvious that it's
not a coincidence if a book published in 2000 is titled
Millennium. After all, the authors would've known perfectly well that it would be published in that year, and it stands to reason that they would've chosen its story emphasis accordingly.