this is one of the craziest stories i've read. hackers are absolutely going through and testing low-entropy generation tools, there was a defcon presentation on it a few years back so they absolutely are doing it now.

As far as their entropy, they could have taken dice from a gaming store or dice from a real casino, rolled the binaries themselves and generated very high entropy that way.

You still need a computer to produce the checksum but the entropy can be produced through nature... a shitton of dice rolls and be way better off.