Hey thanks for the detailed comment!
The red cube is meant to block you. When you have a 3x3 grid with no moveable space in the middle, it's not clear that you can't move to it, so we added a block to indicate that you can't move there. It should have been in the tutorial (which was a bit of an afterthought), but ideally, I'd like to remove it altogether - I don't think it fits very well thematically.