I agree with other posters that education, race, the way that the city lines are drawn, the fact that Austin is a relatively populous city, and the huge flagship campus in Austin all play a role.
I would also guess that, compared to other Southern cities, Austin has a significantly higher share of population that was born outside of the South. I don't have data to directly back up that guess, but anecdotally I know a decent number of people who have migrated to Austin from the Northeast, and I know that a lot of people have migrated from California to Texas.
We know that there's a major
partisan/ideological major difference between Southern whites and non-Southern whites and I would guess that that remains a factor even for non-Southern whites who move to the South.
