[offnominal]

The survey was done across California -- not just SF and LA. Either way, wikipedia claims that 37.7% of SF residents were born in California which is slightly closer to 50% than the 25% figure you quoted (https://en.wikipedia.org/wiki/Demographics_of_San_Francisco#...).

The survey also states that "Most participants (87%) were born in the United States. ... Two-thirds (66%) were born in California."

I still don't understand why the survey is statistically impossible.