I notice that's unsourced.
Everything I've seen says that Rudy took NYC out of a deficit situation and left with a surplus.
My understanding is that NYC prohibits the rolling over of a budget surplus from one year the next. The City effects a rollover by prepaying future expense (usually debt service). While this may reduce the future debt service burden, if also means the surplus is spent and no longer appears as a surplus.
Unfortunately that's a common occurance. Frequently it's dealt with by simply spending the surplus.