The lomdishe question that circulated afterwards was - Is their eating considered an aveira? They were clearly not at fault but maybe it is still considered an aveira bi'shogeg and not אונס. [Of course we would also have to understand the nature of an aveira committed באונס].
The mishna in Parah [12/4 that I learned li'ilui nishmas Naomi bas Zev whose yahrtzeit is beis shvat - may this Torah be more of an ilui for her pure neshama and please do a mitza in her zchus on her yahrtzeit] says that if the purifying waters and ashes of the Parah Aduma were sprinkled on somebody and afterwards the person entered the beis hamikdash and unbeknownst to him the water was pasul, he is exempt from bringing a korban [for entering the beis hamikdash bi'tumah]. From this we see that the person is considered a complete אונס [for if he were shogeg he would be חייב קרבן].
However in Yevamos [87b] it says that if a women gets married based on the testimony of two witnesses that her first husband is dead and then one bright April afternoon her first husband walks right by her on 86th and Broadway [carrying a Fairway shopping bag] she has to bring a korban as a kappara for being intimate with her second husband. From this we see that she is considered shogeg and not אונס.
סתירה!
The achronim work hard to resolve it. If you are industrious you will find who they are and what they said.
Rav Moshe Feinstein had an interesting שיטה. He maintained that if you rely on a kosher witness based on the rule of עד אחד נאמן באיסורין and if it turns out the food wasn't kosher it doesn't matter - the food you ate WAS kosher. The נאמנות of the עד אחד changes the חפצא of the meat to being kosher!!
THAT is a ROCKIN' chiddush:-)!
According to that the people at the wedding hall did no aveira at all - not even באונס.
Lamdanim - I await your educated insights....
Isn't it beautiful how we turn evil [i.e. the caterers deeds] into Torah!
Love and blessings:-)
