Why is Texas Tech and not UT, UH, or SMU the one with the lowest unemployment and lowest unknown rate?
I would guess that it's because they are the only law school located in the entire western half of Texas. A graduate of TTU would be more likely to take an offer throughout west Texas than would a graduate of SMU, Baylor, or UH (likely more focused on positions in Dallas, Houston, Austin, etc..)
The average first year income of a TTU graduate is, however, lower than these other schools which could be explained by them taking lower paying positions throughout the area (which would likely include El Paso, Lubbock, Midland/Odessa, Amarillo, Abilene)
This is all just a wild guess, btw.