IDK, it could be a mix of things, I guess. Like maybe since this is written for a Japanese audience that taking an American viewpoint to it means that I found a lot of things that look like it should disqualify it as a romance (or at least like it is purposely not going there), but in Japanese culture, it wouldn't. Like a 7 YO and a 20 something isn't a strange couple or that a father/daughter isn't an unexpected pairing... that just seems weird to say.
Though in American culture, a child having a crush on a parent is not that unusual in little kids, but it is just treated as a cute phase, not a call to action.