I've recently been reading posts in which people discuss the flashback to the duel between Roche and Iorveth as if it had really happened.

Up until now, I'd thought that Roche/Iorveth was just saying a bunch of bull in order to seem more kickass. I mean, when the flashback began and Roche was there, in the woods, alone, and Iorveth just happens to step out the brushes, alone as well, and then the way in which the victor melodramatically spares his opponent before letting him go...

'The Witcher 2' being so INCREDIBLY un-cliche and down-to-earth realistic (For a fantasy story), I thought that this was just CDRed making a funny jab at Roche/Iorveth's ego, because if such a duel HAD taken place I'd consider it a shockingly unrealistic event compared to what came before it and what came after. I was willing to believe that maybe the two had clashed, and that the events that we see are only as the victor DESCRIBES them.

I guess it would realistically be *possible* for Iorveth to have been scouting ahead on his own, for some reason, and Roche to have become aware of this and decided to face him alone - or maybe they arranged the duel?

Can someone please explain to me whether that duel really took place?

That's why I believe it didn't really happen. The only possible time frame for this is exactly between the encounter at the elven bath/statue and the mission to exit/leave Flotsam. I always wondered how that should be possible.
Also, both Iorveth and Roche seemed way to eager earlier to actually kill each other, if they had the chance. And then they just allow their nemesis to leave?

Well, I agree it's weird the flashback happens even if Iorveth was taken captive, but since you can 'lose' the duel in either scenario, it seems strange to me if it was just a made-up story. I mean, why would Roche (or Iorveth) make something like that up, where they lose a duel with their arch-enemy? So I do believe it's real, but the fact that it triggers even if Iorveth is on the prison barge, must be considered a bug or scripting oversight.

It really took place. It would be remarkable that both characters lie to you (depending on which path you choose) but they happen to choose to speak the same lie.

Also, if you choose to lose the fight in either side, the characters will tell you they lose; so it isn't a winner lying either; and why would they lie about getting their asses kicked?

You're right, that would be weird.

But it just seems so... so unlikely. I mean, these are the commanders of their (Albeit comparatively small) forces, facing each other alone in the forest. It almost even seems like a forced cliche.

Maybe they weren't really lying at all, but simply exagerating the story to make it more dramatic, due to their own egos? That was my second thought, as the scene also seemed somewhat grainy, as if it were more like a tale than a flashback to an event.

To be honest, this duel really doens't fits in this game. Somehow humiliates the other side, making it extreamly week and lame:
-you finish off Roche/Iorveth in one second by two simple click, without a Mighty fight like among pros (never in the game can you make such fast and simple kill/disarm, its almost depressing)
-After such a "tiring and long" fight, there is that superfluous winners speech full with arrogancy and pejorative phrases(Roches is the most incredible, almost lame). Like you had beaten your lifelong enemy. Though, lifelong enemyes should be beaten somehow...a bit harder than here, so there is no way that reality is included.

Both sides have their strength and weakpoints both in mentality and ideals.So none of them should undisputably trample down the other in case of choice. You shouldn't hate Roche just because you choose Iorveth, and vice versa. After this particular duel, if you choose Iorveth, you feel like you were saved by a weak windbag from prison, who doesn't even deserves to be your companion. He saved your life, anyway, but you have to dishonor him.
Besides, I don't think that all of you were so sure about who you will choose between them. This should be a hard choice, and shouldn't spoil the other option sympathy.

Because of these and of others mentioned, I really think that these imaginations are purely long awaited boasts,not facts. And fit in both ways.

While I disagree that both of them lied about the duel, I do agree it should've been more... spectacular, I guess? But then again, a swordfight is a swordfight, it may not last that long even if both sides are ~legendary warriors~. It still was a bit too short and a bit lame. I want a rematch. Hmm. Roche is still shown in good light even in you go with Iorveth, especially in Act 2 when you get to kick some ass together. However, if you choose Roche, you don't get to see a single positive side of Iorveth. And that's alright.

The choice is really tough, as it should be :)