I don't think Zoey didn't like him romantically, it's more that she didn't think it was the right time for them, between her dealing with all the stuff with her father and (at that time) Zoey being Max's supervisor. But that roadblock was gone and he showed a different side to himself--it was a turn-on.
That said, I don't think she's made up her mind/heart between Max and Simon. She likes both of them.
I didn't feel like the lines were distributed randomly. Despite the song being a series of nonsequitors, they fit the characters perfectly.
Like so many others, it just took the first few notes of this to get my crying. Perfect, perfect choice.