Sounds like they made a mistake and genuinely believed it was a veggie burger. Not condoning the behaviour but I believe mistakes do happen in catering. The simple thing would have been to simply not eat it. If you didn't like the smell of it ("like something had died") then that alone sounds like a reason to ask for something else. My brother and his family all have different food allergies that require attention and the option is to not eat something they're not sure about. My brother in law was given pork by accident on a dish (the name of the bacon bits was a fancy one not easily.recognised), he just asked for a different plate. The fact that you're celebrating a lounge being knocked down over a confusion over a burger makes it sound like you're making a mountain out of a molehill. I'd have just registered a complaint with the duty manager there and then.