Was this in DirectX or in OpenGL, and on what graphics quality was this?
I think what I am seeing here, is that Steam somehow overwrote a texture in the game, and this happened to be the most important texture: the one that ends up on the screen after post effects have been applied. Which is why my guess is that this is Medium or High graphics quality. I think it is a Steam texture, because it mentions shift+tab.
Is this something you had more often, or just once?
Thanks for reporting this one! Never saw anything like this before!