It didn't say that walls would be stronger than concrete walls. It said that the bricks were stronger than concrete blocks. I would say that this is due to some shit tier "test". Like laying each one down on its side and putting it in a press. The plastic is already compressed and laying flat so it will take higher pressure to break it than a 12 inch block laying on its side with the air space there ready to be crushed. It all depends on what kind of "tests" they used to determine strength.