As the abstract leads with, PCG doesn't claim to be to be a cryptographic PRNG, so this is more of a fun exercise I guess. They managed to break the harder pro

As the abstract leads with, PCG doesn't claim to be to be a cryptographic PRNG, so this is more of a fun exercise I guess. They managed to break the harder problem of reconstructing the seed if the constant increment in the PCG algorithm is unknown in 12500 CPU-hours. They expected around 20k CPU-hours so got lucky it seems. So for being a non-cryptographic PRNG it doesn't seem entirely trivial if the increment is unknown. Certainly far from cryptographic strength of course.