Asterion hadn't wanted to bother Erato during Christmas, so he waited until early January to contact her. They had been texting back and forth and he had found out she was at home and he had decided to surprise her by showing up and bringing her present over. The present which Ariadne had gone to purchase covertly because she was the very best sister.
He hoped this surprise was a good one. He hoped she wouldn't be upset with him for coming over. He had bought her some flowers too, since that is what people did. And then he showed up at her doorstep and knocked.