Does this guy sound like hes just kidding around?

Maybe. Maybe not. A lot of guys like to keep their options open. So maybe he wont start anything with you, but imagine this. You break up with a guy, and he just shrugs it off, pulls out his phone, and makes a date right there. Kinda makes it hurt less for him and more for you. A lot of guys try to have a few "possible" girl friends around, in case of a break up. Or he could just be interested in cheating on his gf, or dumping her for you. Or maybe hes totally loyal and has not interest in anything other than innocent flirting. Why not just ask him "Hey, is there something more going on here? Because I know you have a gf, and I feel like you flirt with me a lot."