Feel free to compare images and videos of '22 and '23 vuelta. That is no way merely a 1 kg difference. And the 6kg was obviously jokingly in reference to Vingegaard. I also don't think it is very likely to beat Ganna on a 50k* flat TT, weighing just 1kg more than your ideal climbing weight, that seems highly unlikely to me, but that is just what i believe.
I think that this is exactly why he bonked in the Vuelta. Normally, when you're either not in top shape, or tired/overraced, you will start to fade harder and harder. This didn't happen, since the very next day he was rejuvenated and rode the rest of the Vuelta like a maniac Duracell bunny. So the explanation lies elsewhere. As some other people already pointed out earlier in the thread, the symptoms (completely bonking, not being able to put power on the pedals but being completely fine the next day) were much like that of a "hunger knock". But it happened early in the stage, so it's almost impossible for it to have been due to not eating (enough) that morning or during the day.
A forum member here talked about the lack of glycogen, which is what you also experience during a hunger knock. Then Dumoulin said in a podcast that it was his belief that Evenepoel had not eaten enough the days leading up to stage 13. So in my mind, all of this makes perfect sense (and it was exactly what i feared before he went to the Vuelta). He was too heavy coming out of the WCC ITT, either tried to lose weight too fast, or/and likely even during the Vuelta. In combination with trying to keep up with his rivals, and actually burning more calories due to his weight while eating less. This explanation makes perfect sense, and i'm quite convinced this is what actually happened.
(* especially for Blue Fridge Tree i would like to point out that the exact distance was 2200 meters less than 50k)