They're not all from the TX, but UTSW in general has a lot of strong residents from TX who want to stay local. As for the death, I asked a friend about that a while back, it was actually a more complicated story than the one-liner. Apparently a very psychotic and aggressive patient came to the ER for chest pain, where a triage nurse sent him to the psych ER without being medically cleared. Once there, he wouldn't cooperate and never mentioned his CP, and then suffered a massive MI. I'm not sure in a situation like that how feasible an alternative outcome would have been for the psych department in that context. Either way the whole psych ER and ER workflow changed after that incident.
As for Parkland itself, it's a typical large volume county hospital (i.e. old, not pretty). The new Parkland though sounds ridiculously nice. They're also building a brand new University Hospital as well.