No it's not. When the sign on the door says "smoking allowed", you have no expectation. It's not unreasonable for you to depart.
What is unreasonable is for you to assert some right which does not exist.
I think you are missing a key fact. The champions of the Smoke Ban in Austin are band members and waitstaff.
As a customer, I agree with you 100%. I have a choice on what resturant/bar I go to. I am free to go in, or leave. My choice.
However, the waitstaff and band does not. This is their job, they have no choice but to go to work. They are claiming the same protection at the bar, as is given 'at the office'. From THEIR perspective, I think they are correct. My argument has been (and continues to be, in this instance) from the waitstaff's point of view.