I haven't RTFR but while yes he's said he's involved, I wouldn't expect he'd have to tell them WHAT his involvement was...that's the prosecutions job.
The ruling (from accounts) seems to be separating the providing of the password from the contents of the drive - which is an unreasonable search. If they already know what he's done from what he's said, they could easily give him immunity for anything else found on the drive except what backs up what he's already said - then there's no 5th violation.
Also generally speaking, the warrant to search a drive has to be pretty damned specific, so if they already know what he did...it seems odd to request access to the drive.