"That isn't a reason." It isn't even an excuse. He cleans his whiskers with a paw, careful not to allow the bell on his collar to make a sound. "It's none of my business, I'm sure, but shouldn't a good little Daybreak witch be warding herself against the temptations that may present themselves on this fair night?"

As a fae bound in service to Circle Midnight, Mogget always knows a Circle Midnight witch when he sees one. This witch is not Circle Midnight; ergo she must be Circle Daybreak. So he's guessing, but it's an educated guess.