Why is "at least a small tilt" between rotation and magnetic axis required by models of magnetic field formation? I saw something I don't understand in the Gizmodo article Cassini's First Grand Finale Images Are Stunning—But What Are We Really Looking At?. In a quote of Caltech Professor of Planetary Science Andrew P. Ingersoll, it is suggested that a it necessary for there to be at least a small tilt between a planet's rotation axis and magnetic axis.

Ingersoll mentioned the final Grand Finale observation he was looking forward to most at the very end of our conversation, which could solve an ongoing mystery of the planet’s formation. Saturn’s magnetic field has a very unusual property in that it’s “axisymmetric”—it has no tilt. That’s weird, because the math behind planetary magnetic fields requires a bit of tilt.
“How does a planet generate a magnetic field? The off-axis tilt is sort of part of that whole theory and if there’s no tilt at all, well, it will be interesting,” he said with a chuckle.

Is there a way to understand why a tilt is required in current theories of planetary magnetic fields?
"Tilt" is a consequence of a convecting metal inner core....not a "necessity". In the earth's case, that tilt has, over time, wandered from 0 to 180 degrees, sometimes with some temporal regularity, other times completely randomly. The science writer likely poorly paraphrased Professor Ingersoll's curiosity regarding the existence of a molten metal core deep within Saturn.