Sarcasm is an adjusted stress reaction.

I thought that this episode implied what had actually upset the Doctor in "The Snowman": after "Manhattan" he travelled with River for a time until he realised that he'd run out of actual meetings with her before the Library and her death.

I thought as well that the idea of River "projecting" herself might have been an attempt to make the fans who read "Forest of the Dead" as her being "trapped into domesticity" happier.