I think -30 isn't because he hates her, since even when it was in the negative he looked pretty fond of her even if a little shy, but because it's a romantic love meter. He literally can't see her as a love interest at all at first, perhaps even really thought of her as a sibling, and yet because she continue raising flags with him, he started seeing her as a 'girl' not a 'sister'.
If what she wanted was a brother instead of a lover then she messed up big time then