If you look very carefully during the training room scene, you can see that he does have some burn scar tissue on the right back side of his head, they only showed it for a moment that I saw but I did notice it.
Overall I liked the episode as well, and I was skeptical on whether or not they actually removed CH's inhibitor chip since they basically cranked it up to 1000% during that first episode. Maybe its still affecting him somehow and next week's episode we will see him finally come to terms with what the Empire is doing and he'll re-join his bad batch brothers.