From the article:
The use of the term "seize" implies that the Feds were able to get a hold of the coins without the owners consent. However, while no exact details have been released, the prevailing thought is that it was done through a sting operation where the individual willingly sent the bitcoins to the Feds and they are now keeping them, thus the "seizure."
Of course, the histrionic girls on this site would have you believe that the Feds used some technological magic to go in and take the bitcoins from his wallet without his consent.
ETA: And in case LSURussian is right in his assessment, then perhaps another possible scenario is that the Feds physically seized a computer where the bitcoins were stored. However, if they were able to "seize" them with that method, that would mean that the owner did not encrypt his wallet.
But there are no details being released as far as I know, so LSURussian shouldn't be speaking so assuredly.
This post was edited on 7/9 at 3:35 pm