[Moonman62]

The Browns are an example of what demographers say appears to be an unprecedented phenomenon -- even in a good economy, more people are leaving California for other states than are arriving from the rest of the country.

They must not be counting the illegals.

[Michael Bluth]

"They must not be counting the illegals."

I think you mis-read the text:

The Browns are an example of what demographers say appears to be an unprecedented phenomenon -- even in a good economy, more people are leaving California for other states than are arriving from the rest of the country.

Of course illegals were not counted. They do not "arrive" in California from "the rest of the country".