Yes it is, because there's no rule saying mere colour/texture swaps actually have to be referred to as alternative costumes, since "colour/texture swaps" actually define them much better. To me, it's only an alt costume if the actual model is different, like with Hoodie Mac (who will have a slightly different entrance animation too).
And no, he isn't a different model.
-The wireframe skin is just recoloured green skin, with the opacity in some areas greatly reduced, making it possible to see through.
-Lack of face is simply removing his eye texture, eye brow texture, and lip texture. He still has his facial features modeled in though, you can see it in his 5000x5000 render.
-His hair and clothes are just cel-shaded to give that effect of a more limited colour range.