Yeah I think that although he doesn't know Billie, he does know that Logan likes her and hangs around her. Logan just doesn't know it. But I can see Zach being one of the reasons it took Jackie most of last year to start trailing Logan and finding out that he was hanging out with Billie.

Zach: Broken bottles? Seriously?

Haha do it Billie! I think everyone would get a kick out of it.