That's because the studies are based upon "sales tax receipts" for all bars and restaurants. including fast food joints and other places that didn't allow smoking even before the ban. Also, the studies focus upon gross receipts and not net profits. A bar/restaurant may be selling more food at the tables, but less alcohol at the bar. Revenues are up, but profits are down because the profit on alcohol is hugh compared to the profit on prepared foods.
Point taken.
The slicks in my former home city (NY) took that poll on St Patrick's Day, probably the heaviest day for bars in any metropolitan area.