Ah, no, see, we aren't talking based on observation of this actually happening. We're extrapolating based on observed mechanics. I don't imagine anyone owns any provinces that are getting much more than +6.0% autonomy growth by distance, so we wouldn't be seeing the sort of extremely low unrest that might emerge once you start getting into double digits. But we can still do the maths for what happens at higher autonomy levels.
I mean, unrest adds to autonomy growth at a 2:1 ratio (I think, though it seems to be based on last turn's unrest, maybe?). So setting all other factors aside, a province with +10% autonomy growth by distance is gonna end up with an equilibrium unrest of -20%. +20% by distance = -40% equilibrium. +50% (not sure that even a province on the other side of the planet would get this modifier) = -100% equilibrium unrest. Nobody is experiencing this yet, but that's no reason to ignore the issue.
E: No, wait, looking at it again, I'm not sure what the relation between unrest and autonomy growth is. It doesn't seem to follow a pattern? Okay, so, it does seem like unrest*0.5 is the default, but changing faction opinion modifies that in a strange way.
E2: Also, it looks like the autonomy tab doesn't add up properly. The stated change doesn't seem to include the population modifier (although the actual change does)