I think you did everything right. We have experienced a similar thing but didn't get called out on it, so no drama except for us feeling uneasy about the situation. I asked about it in a thread and the consensus was that meeting for dinner or drinks before going to a club or party implies greater potential for play. http://www.swingersboard.com/forums/...w-couples.html
I think it can be hard because many people do like to nail down their play partners for the night so they don't have the stress of figuring out how to pair off later. Then they feel they have to cling the whole evening to fend off other "contenders"