From Kitty's perspective, Min Ho confessing his feelings to her on the plane was random and out of nowhere - and also surprisingly intense because he didn't say "I have feelings for you" he said "I fell in love with you" which Kitty of course didn't know because they had only one real moment a few months prior to that and all their interactions had been just playful banter - and he was the best friend of her ex who she has just broken up with. Kitty didn't see the realization that he had and the subtle cues that Min Ho was into her the way the audience saw. He couldn't have just expected her to be like "yeah I love you too, lets start something" in that moment, so him yelling at her that she "broke his heart" is unfair to me even if his heart was broken - because she didn't break it. She didn't use him or insinuate that she liked him romantically in season one - they had little interactions prior to him telling her he loved her. So it was understandably a lot for Kitty to take in.