>>55430641Eusine could see Suicune outright ignore him in favour of you. He may not have been happy about it but he knew Suicune made its choice independently and he just wasn't worthy.
Kieran sees you sneak off with Ogerpon, having fun adventures behind his back. From Kieran's perspective you just seduced Ogerpon, add to how upset he felt that he considered you a friend that betrayed and lied to him, particularly about a Pokémon you knew he had an obsession with. He feels extra betrayed that he's the one who defies his grandfather and clears Ogerpon's name so she can live in Kitakami and interact with the villagers like she always wanted, and you say lolno I'm catching her. Even though it was what Ogerpon wanted, Kieran still sees you as a liar who deceived him so he's not going to believe that you're not also deceiving Ogerpon.
tl;dr Eusine can appreciate your character's earnest personality making you worthy of capturing Suicune. Kieran sees you as a filthy liar who's probably deceiving Ogerpon just like you did to him.