Looks like a missing piece to me.

Smaller cube sticking out of the larger one! Really enjoyed that one, thanks!

Thank you.

Missing initially then on further examination I can see both options.

Missing piece, mostly because the angle shows that the smaller object sticking out wouldn't be a cube.

Two views of the flat resulting image:
right in the lower corner of the room is a small cube
the big cube missing the right front upper small cube
Thanks.