A Texas attorney could advise best, but your post remains open for two weeks. Many facilities are taking similar measures in these difficult times. They may not be explicitly telling people to wait in their cars, but they take in only limited numbers of the public into doctor waiting rooms, post office lobbies, food marts, and other locations. There could be local or state laws in place (and that's something a Texas attorney could explain better) that require social distancing in confined places. Current public health concerns override the inconvenience such measures create for the public. Good luck
Tim Akpinar