Could the portal/door picture be a reference to the original Richtofen killing Maxis?
And perhaps the Shadowman has visited this universe's Sam before, perhaps telling her of the universes he is aware of. That could be how she found inspiration for the original storyline (Origin's cutscene Sam).
And maybe the forest picture is reference to the forest where the main menu for zombies and the death scene takes place. Because I feel like it has more significance than just being a dynamic menu forest. Or they would've just made a zombie submenu like the first Black Ops.