This idea is ingenious. It might be alittle difficult to clean, but it is ingenious. As the bright minds on reddit have pointed out (because someone is wrong on the internet), this is actually a Duplo wall. But, since Duplo is a subset of LEGO, and, in the end, regular sized LEGO bricks can be attached to Duplo bricks, it’s all technically correct, (the best kind of correct).
I gotta say, if these were attached to the walls correctly, this could be pretty easy to make, only cleaning it would be hard, but if they could come down easily, then just put them in the bathtub.
The only thing is that from this photo, it looks like a parent has been helping, since that window is pretty high.