It depends how it's set up. Often a block will reserve a certain number of rooms for attendees, to ensure people will have somewhere to stay close to the conference site. Usually any unbooked rooms in the block get released closer to the event date.

Perhaps Flock would say that since they were denying the journalist a pass, they should also deny them the room block discount. The hotel could just charge the journalist the difference rather than cancel their room though.

That comes with a contract between the hotel and the block holder.

Also holding rooms for that block, though.