apushatayid,
Unfortunately your challenge is not quite a fair one, because very few details have been provided, other than “treif restaurant” and “non-Jewish party.” Obviously when you brought this to your Rov you provided him with far greater detail than you brought here.
I would like to bring to the table two thoughts that I have yet to see presented in this discussion:
1.) A Rov tells a person what to do based on how the halacha applies to the person’s specific situation, which is often very complex. Therefore, rather than bashing somebody’s Rov when his decision sounds surprising to us, we should realize that we do not have the full picture that the Rov was given. We might not even have the full picture of what the Rov said. For example, apushatayid stated that he was at the party for 45 minutes… no wedding party lasts 45 minutes, so obviously there are details in his case that we don’t know. That said, based on what was provided (which is noted to be incomplete), it sounds like a possible M”A issue to me because of the treif restaurant. How is it problematic even if no Jew sees? Imagine if one of the partiers is a boss at a company with Jewish employees. He later asks the Jewish employees to meet him at the same treif restaurant for an after hours social event, and when the Jewish employees say they can’t come, the boss says, “well just the other week at a party I saw an Orthodox Jew there…”
2.) When a Rov tells us what to do in a specific situation, we cannot take that decision and apply it to different situations ourselves. In other words, what a Rov might say regarding the non-Jewish parents of a ger who dropped in on Yom Tov cannot be applied to inviting non Jewish co-workers for a Yom Tov seuda. Taken to an extreme to make the point, if a Rov tells someone not to fast on the 10th of Teves because he has a serious infection, that person cannot say the following year, “my Rov said that I can eat on the 10th of Teves!”