Outside in the hall, Karyn quickly said (so Jon wouldn't hear it) "I wish that for the last three years there's been a boy who's very much in love with Jon and his name is Steve Farber." Jon wished for the most popular girl in school to be in love with Karyn, so why not have the most popular guy in school to be in love with Jon?
By the time Jon made it out into the hall, he was able to notice the stone glowing, so he knew that Karyn made a wish. But he didn't hear what the wish was, so he had no idea what could be different.
"So, Jon," Karyn said, turning towards him. "Have any problems with Steve Farber lately?"