You two were rivals. Both of you. You had a secret crush on him, but believed he wouldn't like you, and he liked you in secret, thinking you wouldn't like him. You both had wallpapers of each other, you with a picture of Scaramouche, and him vice versa.

You two accidentally mistaken each other's phones, and as you both open the phone and look at the lock screen, it was both different.

you two went back to the classroom to exchange phones, before Scaramouche brought up the sudden question,

"Why do you have a picture of me as a wallpaper?"

You should be asking the same thing, but hey, he asked it before you.