Hi!, the person who is speaking is asking about the reason why the other is so smartly dressed: You could translate it, in this context, as: "how come?" ("why?") "¿Y eso?" really means "¿Y eso a que es debido?": "What's the reason for that?"

Hola, Y eso ? means : and that ? That´s elegant...or...what an elegance...and that? Do we have visitors?