I have seen a lot of interesting and funny RNG issues, but this is one of the most sophisticated exploits for the least payout. A wonderful work of art.
RNG vulnerabilities are usually really bad in terms of the systems they compromise. It often means exposure of keys, huge numbers of jailbroken devices, or something similar. Making at most tens of thousands of dollars in Minecraft with one is sort of cute and fun in comparison.
Of course, I could be underestimating this by a lot.
Yeah, there is a big class of "RNG bugs" where someone uses a non-cryptographic RNG for secure things, not realizing that those things are supposed to be secure.
The classic example of these is a password manager that gave out recovery codes using a PRNG. This is in that class.
While a CSPRNG would have solved this problem, it also would've created a new one: much slower chunk loading and random item placement, which would have greatly slowed down the game simulation, and thus tanked framerate and playability. As it turns out, the right solution is to use multiple, isolated non-cryptographic random number generators with distinct state. That way, even though you can guess the state of one of them, it doesn't give you any insight into the others.