suppose the data were generated by a csprng with 256 bits of state. then in fact there are just slightly more than 256 bits of entropy there (prng state plus the length of the generated file). only, you'd have a snail's chance in hell of actually finding that seed

If he really wanted to make sure he kept the money, he could just use a hardware RNG. I don’t know how common they were in 2001 but you could probably even generate some practically unpredictable random numbers using radio noise.