Heck, I would not care at all and would wonder about the reasons that someone would feel it necessary to post or tell someone about a mistake at that point. I even left in a crazy mixed up block "just because". I saw people taking pictures of the overall quilt and no one at the guild pointed out the huge not to be missed mixed up block.
Either the person will not care or you could really hurt others by pointing out mistakes that either cannot be fixed now or are pretty minor. Kind of like saying your baby is ugly or pointing out an obvious birthmark. Would anyone do that?