All the "faux-paint" portraits - including this one - are created with vector bases in Illustrator and then the facial features + details are painted on with digital brushes in Photoshop. So sort of.
I uploaded a deviation to show the progression/building of my original faux-paint Princess Zelda piece; the process was pretty much identical for this one, too. You can check it out here if you like:
fav.me/d6tb91u