In the wrong for what?
The only thing I have a serious problem with is coercion. That sort of thing should not be tolerated.
If they don't want to honor a discount, well, so be it. It's not the first time that sort of thing has happened. The reason why we KNOW about these sorts of things is that people talk about them and are not COERCED into keeping quiet.
Otherwise, there are two sides to this story and neither side is 100% anything, right or wrong.