Eh, I remember when this was coined, and it was specifically about people graduating college at the millennium. Granted, I thought then (and still think) this was a weird benchmark to use. But the whole thing is dumb.
You may be misremembering, or perhaps you meant graduating high school? People who graduatedcollege in 2000 are not considered to be millennials as they were been born in 1978 or 1979.
Hmm, I'm pretty sure it was college, because the topic of conversation at the time was the job market facing these new graduates and how they were the first cohort that could not necessarily expect to "do better" than their parents.
