When I'm invited to a birthday party, be it kink folk or not, I expect the usual birthday party theme. Was there any indication that the invite was for a birthday/kink party? I'm submissive and other than giving one or two birthday "taps" I doubt that I would want to paddle another submissive.

My reaction would probably have been the same; head for the door PDQ as this wasn't consensual.

If you feel you overreacted and are embarrassed, prior to attending another munch, etc., I would contact the submissive and let her know you were caught off guard. Perhaps she can express this to others who may have felt "your" behavior was rude or odd and you guys will get over this.

I wish you the best.