The specifics of this one incident are not all that important. It is one anecdote among many. She never named the person in question; she is not trying to publicly shame him or anything of the sort.
This isn't something where we need to hear another side of the story, other than maybe from the conference organizer (though even there, she's not trying to blame one conference or one organizer, just pointing out that this is something that is frequently overlooked).
If you have any decent amount of life experience, you have seen something like this happen at some point. There are men, who sexually harass women, and don't take no for an answer. In any large enough group of men, you will find one at some point. Have you never met someone who has done such a thing? Never met someone who has been a victim of such a thing? Actually, even if you think you haven't met such a victim, you may have, since most people don't like to talk about this sort of thing.
The story is that the conference didn't have any effective way of dealing with the situation, not the details of what actually happened. This sort of stuff happens. The question is, what do we do about it? Do we ignore the problem, hide our head in the sand and hope it sorts itself out? Do we say "well, if you don't like it, don't go to conferences, or don't go to meet ups at the bar afterwards"? Or do we try to do something about it, make it clear what sort of behavior is acceptable and what is not, and tell people that if they cross that line, they won't be welcome at events any more?
And your two alternative readings are quite a stretch. The second is "Clash of cultures; open-marriage dude meets conservative girl." I know many people with many alternative lifestyles, open marriages, polyamorous relationships, Master/slave relationships, and the like. In none of those cultures would this behavior be considered acceptable. He didn't take no for an answer; that's one very clear signal that he is ignoring, and no matter how open you are in your marriage, no means no. He also, after going far beyond the line to someone who had already said no and stating that he's in an open relationship and would have a threesome with his wife involved, went on to call his daughter a slut. There is no sense in which that can be considered healthy; that is either blatantly hypocritical, or a creepy sexualization of his own daughter, and he clearly has some issues.
Your third reading is also incredibly uncharitable. Here is someone who is posting under her own name. She is putting herself out in public, describing a rather personal and traumatic scene, under a real name. But you will notice, she has not named the person in question. She has not named the conference in question. She has not named the conference director in question. It is clear that she is not trying to smear anyone. All she is asking for is that we think about these kinds of issues, and have an answer for how we will deal with them in the future.
So, yes, it is worthwhile to take stories with a grain of salt. Think about whether someone could be lying; what they would stand to gain, or who they might hurt. But really? Does she stand to gain anything here other than a little notoriety as that person who was sexually harassed and spoke out about it? Does she stand to hurt anyone? As far as I can tell, the greatest thing she could gain from this is a more well defined sexual harassment policy at more conferences. Would that be a bad thing?
So, even if this was all a misunderstanding, or made up, do you really think that this isn't an issue? That we shouldn't have any way of dealing with this kind of issue?
The least charitable way to read this is that she is simply trying to make the issue of sexual harassment at conferences sound more important than it actually is. I know, from personal experience, that this is a very important issue. People like she described are extremely harmful to a community. Even if her story was entirely made up, there are people like that out there, and you need to have an effective way of dealing with them or you will get hurt or allow others to be hurt.