In the first one, his body was already reacting to his soulmate. It's just that when we was still the Black Dragon, he did not know the proper concept of human genders. He only knew that women were able to give birth and men were not. So he directly assumed Chinagi would be a woman after rebirth. Although this misunderstanding did indeed hurt Yasu, the fact that Black Dragon was fighting his urge to be with Yasu shows that he is extremely loyal to Chinagi.
Maybe mr black dragon read his story from a translation group that flipped pronoun genders all the time. (⊙…⊙ )
I don't know if it's translation's fault or storyline's pacing weirdly but it's totally nonsense that in that first story seme hold his soulmate many time in past life but he still didn't know that it's not she but he , the guy beside him was his soulmate all along of course he didn't told him cuz he said she was beautiful so uke changed lot by reincarnated so he got scared of getting rejected by seme. Second one is little bittersweet but it turned out well enough