Deleting Chapter and/or Trickplay Images

[generic3075]

I'm running 10.10.3, I have /config in the container mapped to /mnt/user/appdata/jellyfin, and I see trickplay images are stored in /config/data/metadata/library in the container. What I don't understand is how that increased the vdisk size so much when it's supposedly stored in the host filesystem.