His comment about Carlotta was primarily redirection, not an indication that he had any desire to harm the woman. He needs Christine to focus on her singing.

The lesson goes well, though he would have preferred to stay behind the wall. Or take her back to his space. There is much potential for interruption with him being in here. And the many ears that lurk in the corridors might overhear and wonder where he's gone. There is also the fact that he's in this room with Christine. Down in his lair, it's comfortable. He knows that space. This is but a small room with very little space between them.

And now she's inviting him to have tea... "I..." he pauses, uncertain how to respond to such a request. "I - I beg your pardon?" he asks, curious really. Because - why?