Wasn't he making pretty decent money, despite how gruesome his performance used to look like? The apartment looks good, the sister keeps living comfortably, with plans to send her to a good university, and the mother is in a coma but taken care of in a hospital. He could also afford to recuperate between the missions. What would be the normal job, anyway? I don't think he had the time to get a good education before he needed to become the family's moneymaker. He's not likely that much older than the high school student sister.
Anyway, this is just the beginning for him, so imagine how high those numbers will be after a while. If there was a mistake, maybe it was the author naming that attribute Int.