You forgot to deflect the sleep.
Anyone who has played Genji for any amount of time knows that Swift Strike stretches his hitbox into the size of a freight train.
Knowledge issue.
At the moment you hear the sleep dart, the Genji is right ontop of Ana. With the way the latency thing works, Genji would still be very slightly in front of the Ana on her screen.
Kind of a dumb luck situation still all-round, but it is amusing when it happens. Does sort of balance out Genjiβs generally incredibly DPS friendly methods.
Balanced