Re: Six months only? House arrest, no jail?
In December 2015, he pleaded guilty to making a false statement and damaging a U.S. Army computer.
It doesn't sound as if there was anything espionage related, only deleting the logs ("damaging a U.S. Army computer") and the false statement on the security clearance form.
So perhaps he was intending to use the thumb drive(s) to backup or copy files about within the organization or something like that, i.e. not to pass the data on to someone else.