The original Seth Brundle got into Booth #1 and the copy that believed himself to be the original was in Booth #2. The twist here was the perfect copying actually worked this time. After realizing this, the clone fully accepted his fate and decided to cooperate with the original's whims even expressing joy at how perfectly identical they are, down to his internal organs, as he is being subjected to an autopsy while still alive which I guess also perfectly matches the original's obsession with this experiment. As to how it ties in with Yuuma's tale - like the clone knowing that only one of them can continue living, perhaps the author is hinting that Yuuma has fully accepted that Hina has to go. That's why we see "Mom" warning him not to talk to Hina too much in case he has a sudden change of heart.