Not very open minded of them. Most arguments have at their root, a fundamental disagreement over who is right and who is wrong about something. I would think those that attend a swinger's party have pretty much sworn off any objective measure of right or wrong.
Maybe she was willing to do something with 'swingers' that she was unwilling to do at home. Maybe she wanted something after the party that was a bridge too far. I'll leave this to your imagination.