Q. When making a seudas hodoa for thanking G-d for the miracle of His great salvation, does one have to disclose to the guest partaking at the seuda, the reason for that act?
A. Mishna Berura (218: 32) mentions that even if there was no open miracle in the salvation, since one was in real danger he has to express his thanks and recognition to Hashem. He adds that one should give tzedaka to those who learn Torah and express that this should be in place of the korban todah one was liable to bring to the Beis Hamikdosh. Piskei Teshuvos (218: 11) quotes Chavas Yoir 70, and other sources for the tradition on setting a seudas hodoyo and there relate, tell and express his thanks and acknowledgment to Hashem's compassion and deliverance. He also adds that if there are reasons why he does not want to divulge publicly what happened to him, he does not need to.
Similarly, Horav Shlomo Miller's Shlit'a opinion is that it is most important to express at the banquet, meal or kiddush, one's open thanks to Hashem for all His gifts, deliverance and salvation. When possible one should explain the reason for the act, in order to properly thank Hashem for His benevolence.
However, if there are reasons not to divulge what happened, one can celebrate the seuda without explaining the actual reason why it is being done.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a