@Isekaijin they weren't talking about from her perspective though, they're talking about from the villages and her parents perspective. Before she confessed to him, did she ever tell her parents or the villagers that she loved him or wanted to marry him? From the looks of the flashbacks, no, she didn't, she had kept it to herself. Because they were bestfriends who spent all their time together and happened to be a boy and a girl, her parents and the villagers assumed their relationship. That is super heteronormative. Also, I am going to point out, nowhere in the flashbacks did it show her day dreaming about getting married to him, it only showed what her parents and the villagers had said, I suggest you go back and read it.
edit: she even straight up says it's because they spend all their time together and NOT because they actually told anyone they liked each other/wanted to get married