I'm not looking at the book right now but the editors wouldn't know what the system was trained on because the developers won't say. I would assume it includes a significant amount dystopian fiction and apocalyptic web chatter, which may account for its grimness.

In terms of prompts the poems in the book were unedited and minimally prompted--by that point they'd just asked the AI to speak in its own voice. It's worth reading to get a better idea of how some of the poems could have been influenced by the editors.