The soccer dude has absolutely nothing in common with her except the "bi-" in front of bishounen and bishoujo. It would be strange if Kaori didn't get more interested in Arima, assuming they continue to play together and encourage each other to get better. They would be sharing not only music but a lot of practice and performing time as well. It's also hard to imagine somebody playing like Kaori would be only interested in the superficial looks of a guy.
The childhood friend aside, you forgot the soccer dude already has like 10 girlfriends. He won't lose to anybody in the romance deparment, haha.