"The DOJ said it was able to seize the funds after an FBI search warrant of one of Lichtenstein's cloud storage accounts found a file containing cryptocurrency addresses and their corresponding private key that granted access to funds stored within."
Which is to say, this isn't how they actually got cought, it's just how the nail will go in the coffin (and thankfully for those impacted, some funds recovered).
FWIW, if you ever find yourself in this position of owning a large amount of stolen crypto, I believe the best way to wash it would be to "robin hood it out" to a bunch of random wallets. You just happen to own 10-20% of the wallets, but the feds now have to try and track thousands of different people over years to try and identify the true thief, and there will always be plausible deniability.