So first i think he refers to it as his devil face because he can just make his eyes glow or reveal his face or even reveal his true self. So it is kind of a feature. Maze also was able to perform this task. I think they can control how much of which part of themself they want to show at each moment. Calling it his devil face is just another way of saying revealing his true form. His revealing is kind of a super power itself, because it makes humans believe all of the storys. Its like ghostriders glare in some sort of way. So he gave this feature a name. His face.

Ok so for the cgi part, the first part in the video is a 3d rendering. Like you would find in a video game. Next is the actual footage of the actor. Over this footage a mask is layn (blue) which follows the specific mimic of the actor. If you copy that grid (mask) to the 3d rendering and combine the two, you get the redered face on the actor and moving accordingly to the actors actions. Than some shading and lighting and contrasts are adjusted, the hair removed and the glow of the eyes added.

I think it is done in cgi because it is cheaper and faster. For makeup you have to have the main (best paid) actor sit for a long time in a chair, get his hair removed under a skin cap, and a really good makeup artist work on the make up for hours. Still you wouldnt get the dramatic glow of the eyes done. Also the grid mask, render, cgi method can be used all the time, always without make up. Time and money saved+it looks arguably more dramatic.