The game's only been running for a year! How are you so far in debt?
My best guess: he got a ton of money from something, then got an event which required him to pay X years income for the outcome he wanted - while the game still considered the ton of money he got to be part of his income for that year. I've seen weird numbers for "annual" income due to one-time things like inheritance, and it usually takes a little while for it to recalculate. If an event fired in the meantime...