Notch uploaded a random short unlisted video to his nizzotch youtube channel of himself saying hi to some random redditor and linked it in a reddit comment somewhere. The video wasn't ever reuploaded anywhere and became unavailable along with all the other nizzotch videos. Since it was unlisted, it was overlooked by everyone who archived the rest of the channel, and no one's ever found a downloaded copy.
https://web.archive.org/web/20200415202710/https://www.youtube.com/watch?v=9-fuwsWTL_8