What does it mean to "kinda meet a girl on the side"?

I have a girlfriend but am looking to make more platonic friends. I responded to an ad on craigslist by a girl under the strictly platonic section. I emailed her and told her I was in a serious relationship and was looking for friendship or someone to study with. She responded "So are you kinda just looking for friends to study with or kinda to meet a girl on the side? I guess I'm just gonna be up front and ask bluntly." What does this mean? I am not a cheater and do not want to be friends with this girl if she thinks there will be something more.