So, i got a new work laptop and decided to use rsync to copy a bunch of stuff from old to new machine.
I ssh'd from new to old machine to verify I could connect the two. Then I ran rsync.
Turns out I never disconnected from the old machine. So that's where I typed the command.
Thus, I just looped from the old machine back to itself, duplicating a directory the hard way. And I filled up the disk.