I thought it wasn't possible for this to happen?
A government gaining physical access to unencrypted private keys that aren't backed up would make those bitcoins vulnerable to seizure.
the coins seized were likely the sites escrow coins, which were probably able to be seized along with the physical servers.
any properly protected bitcoins can not be seized.
for instance, why aren't they reporting that all of DPR's wealth has been seized? he supposed made almost $80 million on the site. so why haven't they seized whatever he has left of that?