[@December]; I assume they would have a different scent compared to some other supernaturals, meaning that she would be aware that Sebastian is different to the others, and that he's something. Zoe doesn't know what Syleste is, she just knows that she's something but cause she hasn't shown any signs or powers, until tonight, no one has been sure about what she is probably except for Sebastian who would of had a hunch of sorts. And now, as of her screaming her lungs out, there's going to be no doubt that she knows that Syleste is a siren; also, it wouldn't be hard for her to put two and two together, I assume that she would have known about Sebastian being one for a bit now, just stuck back and kept an eye on him like she does all supernaturals, rather than approaching.