The world produces four billion tons of cement per year, about half of which is produced in China. For comparison, polyethylene, used for these bricks, is produced at about 100 million tons per year.

In other words, even if all of the waste polyethylene in the world could be recycled like this, it would make, at best, a roughly 2.5% dent in the demand for concrete. (There are aggregates in both cases, so you can't just lean on that.)

It's useful if it offers functionality cement doesn't have, which in this case it seems to. But the idea that plastic waste, in any form, or for that matter any other wastes (aside from asphalt, which was once a waste product), can substantially replace building materials, is mostly a popular misconception rooted in humans' difficulty with large numbers. Comparing the bricks to concrete just isn't really apples-to-apples.