At most airports, the priority security lane includes premium cabin, and whoever else the airline grants priority to, such as elites. However, in a handful of situations, the priority security lane is for premium cabin passengers only. IIRC, SNA is (or at least was) in this latter category. Maybe IAH terminal A is also in this latter category for some reason. It would have been easy enough for the TSA supervisor to explain this instead of being rude about it. What precisely did the signage say?