Several of the security people who worked the door at our convention told us that at the convention that took place there the week prior to ours smoking had been permitted.

I believe you heard at least one of those conversations.

Unless these security people were lying (with no motive), it could reasonably be inferred that the hotel has some choice in the matter... either making the area smoking or non-smoking in accordance with a law or simply ignoring the law on a convention-by-convention basis.