Isn't this kind of similar to Charlotte?
To some extent, but in Charlotte it could just be because the downtown precincts are whiter than the more heavily black precincts that surround them. In Austin, you have the downtown precincts (which are fairly white) voting well to the right of mostly white inner-ring suburban precincts.
Ah. You're probably right that there's something rather unusual or atypical here. What sets Austin apart might be just how heavily White it is compared to other Sunbelt Southern cities, which makes such differences in voting patterns just more jarring.