I was born in 1990. Facebook is not my Internet. When I grew up the Internet was a very fascinating place. Flash games, web forums, chat rooms, peer to peer file sharing of mp3 files and movies. A friend of mine had an older brother who used to give him home burned CDs with software, anime, games and other files, that the older brother had obtained via Suprnova.org and other torrent tracker sites. And me and my friends also downloaded and shared files using BearShare, LimeWire and KaZaA Lite.
So no, I can not agree with the overly simplistic characterization of millennials as thinking that Facebook is the Internet.