There is another point here, and this may perhaps be the real reason why you are unsure about this whole thing. It was something that I have been thinking about from the beginning but deliberately didn’t want to mention right away. You actually kind of alluded to it yourself in one of your later posts.
You started off with the assumption that you were not allowed to be “mekabel” the loshon hora, so I was basing everything I wrote on that assumption. But perhaps based on the way you heard the l”h and who you heard it from and the type of information it was, you were actually allowed to be “mekabel” it. Granted, we already established the fact that it’s always assur to be “mekabel” l”h, so you were not allowed to be “mekabel” it before the event.
However, it is possible that you were allowed to have such a strong “chashad” that combined with what you yourself saw at the event, you were then allowed to be mekabel. This would also be taking into account the reaction that you saw from all of the others present.
That is very different from saying that it is assur to be mekabel but once you are mekabel, you can use that information to embarrass someone publicly. I don’t see how that can possibly be correct.
However, I don’t know nearly enough about these halachos to be able to say whether or not this new possibility can have any halachic validity. It seems to me that this is a complex question and one that must be asked to a Poseik who is very well-versed in the halachos of Loshon Hora and knows far more than what is written in the Chofetz Chaim. And I am kind of wondering why you posed your question in the CR instead of bringing it to such a Poseik (as interesting as I find it).