But this is not the same scene. He is fully naked when he is sat looking at the ocean, then, he stands upm THEN it cuts to this part you mentioned. And true, at this part he is indeed covered up, I enhanced the screenshots of the part you mentioned and it is covered. And he is wearing this because this scene is shot in a very dark shade.
The same does not apply to his fully naked scene on sunlight, looking at the ocean.
And now, since his thong is evident jn the scene you mentioned and not in the one I am referring, do the math.
Plus, you can check it yourself, no evidence of thong in the scene I mentioned, in any screenshot.
And finally, I am sending a picture of one of these screenshots enhanced with contrast, so you can see, I can see, everyone can see his penis, his balls, even his dick head. There isn't a single moment you see any thong line in this scene and assuming it was visible in the other scene, why would they take so much care editing that one? Specially considering its a scene where he is far away from the screen, in a dark environment? And as you said, this scene lasts 2 seconds.
If they edited the thong out, it would make much more sense if it was in the scene you mentioned, where he is closer. Also, the movie is from 2008, editing was not as strong as nowadays, and internet was not that popular, so concerns about this type of exposured were not the same, at all.
And, please... check the picture with constrast yourself... I bet you did not read my thread... I explained everything there.