Oh man... I thought that maybe, just maybe SS used really good sculptors for all their work!
Now I see they're using Zbrush.... why would you use Zbrush for only a "sketch"? It's a program for adding super realistic detail to models.... Why do you need fine details on a sketch? They're just gonna use a machine to carve the model for them...
follow the link to see the site for Zbrush
https://www.pixologic.com/home.php
(How can I tell it's Zbrush? Cuz there's no other 3D modeling program that shows everything in orange with a grey background.

it's true)