Mix of one of the largest flagship universities in the United States, state government of second largest state in the country, a big time music scene, and a lots of tech industries.
Nashville also combines a lot of those things and isn't nearly as liberal as Austin (less Democratic despite also being much less white), so I don't think that fully explains Austin's liberalism (actually, wouldn't the state capital of a conservative state even move it to the right).
Vanderbilt is tiny compared to UT-Austin. And country music is a wee bit more conservative than Austin's indie music scene.
I was more thinking of the combination of several universities (not just Vanderbilt, and more of the academics it brings in than the students themselves- some of whom don't even vote in the state at schools like Vanderbilt and Belmont). Nashville also has Belmont, Lipscomb (which is probably pretty conservative, even at the faculty level, but still), Tennessee St., Fisk, and Trevecca. The differences in the politics of music is probably relevant here. But, my hypothesis is that Austin is so liberal because it is so liberal. Since it has a reputation as such a liberal hipster enclave, it attracts people wanting that lifestyle in a way that nowhere else in the South does.
I think that's it, your last point. FWIW I had a professor in college from Austin who said that Austin is nowhere near as liberal as we all thought. Mind you she was telling a group of Seattle kids this, so she probably meant "guys Austin is not Seattle srsly"
