Add in the fact that hobby purchases are very discretionary and a lot of people are willing to pay a little more for quality/genuine articles and this business is probably safer from simple undercutting than one would initially think.
For a recent example, see the fidget spinner / cube situation, so many copies from so many manufacturers, it was unreal.
No way. The combination of materials and small size are too novel.
Toy manufacturers have the equipment and experience to make small items out of plastic. Cinder block and brick manufacturers have the equipment and experience to make large blocks out of concrete.
No one has the machinery necessary to make tiny concrete blocks like this at scale within a month.
Even if a company took the time to build the setup required to make this product at scale, these things are much denser then the average toy and shipping costs from a cheap overseas factory will eat into the already thin margins.