No, Kazuma is secretly a robot and that white patch is where his fake skin was scraped off by something. I thought we all knew this?
Pixel only gave him one portrait, which shows him smiling. So we have to assume he's a fairly optimistic person, except for when he was like "blablabla Quoe we shall flee the island". Well, he only said that because he wanted Quote all to himself. So Kazuma's probably not traumatized yet. Give him time.