The plants have H2S detection all over the plant. They are required to have an alarm system. They probably had a release, but then went into shutdown mode within a few minutes. If the situation got out of control then you would hear an alarm. A VERY LOUD ALARM.
I wouldn't worry. A high concentration of H2S should quickly be dispersed by the winds. You have lots of wind at night near Houston because of the Gulf. If you keep smelling stuff in the air then you should call the State to investigate. It could be something that the plants don't know about.
FYI, and likely not related to this situation, is a chemical described here:
http://www.bt.cdc.gov/agent/soman/basics/facts.asp
called Soman. Chemical warfare agent. Smells like camphor, or rotting fruit.