In the process of solving the first puzzle (the one in World 2) you learn that the bridge in the picture can actually be interacted with. Using this it is possible to jump onto a particular wall in the house:
Everything in this game seems to have a purpose behind it, may it be to solve a puzzle or tell another part of Tim's story. I can't think of a good reason as to why this wall has this hole whereas the wall in the floor below is complete.
Additionally, the rooms aren't of equal height in the bottom floor... perhaps the floor with the holey wall was originally a single large room?