Like joining a soccer game and finding out half the other team was hired to let you score goals -- not a very stimulating experience if you ask me.
What would be the analogous of scoring goals in the context of a work party with coworkers? Also, I think it would be a bit exaggerated to freak out and leave. Although maybe I'm imagining the situation differently to how it was.
Since you didn't get the analogy: I don't find it enjoyable to converse with people who are paid to deceive me, especially if I find out about it after the fact. I wouldn't mind it as much if the models were clearly identified as such so that I could either avoid them or engage with them knowing full well what's going on. I am shocked you find this surprising.
My bad, I didn't know they were meant to pass as guests! I imagined they would be clearly identified. I agree it's a very uncomfortable situation.