OK! My fault. I thing I got what is wrong. I checked your snapshots list (Droplets > Destroy > Rebuild > Select an Image) and find out that there is no "MEAN Archlinux" option in that list. But I can select the MEAN application (It seams that next time I should read the entire text on that button "MEAN on Ubuntu") on the droplet creation process after or before of OS selection and app won't warns you about it. It seams that selected OS is Archlinux.
This makes an illusion that you creating a droplet with archlinux and MEAN.