It’s truly local, but I’ve heard about it, seen it, along the line that’s South of I-10. Arbitrary line, in my mind, but as a demarcation point, it seems to work.
In “old Austin,” the line was I-35. East Side was “rough,” or, in more politically correct times, “of color,” whereas the western side of that line was predominately “pale.” (I lived in East Austin for several years.)
The first couple of times, I didn’t get it. But my Austin family (kin) loves the South Texas tradition of Xmas Tamales.