^ To add to Zero's post, I believe an injury settlement stems from the fact that a player, after being placed on IR, still thinks he can play (or player sooner than the team thinks). It is obvious the Packers felt Blackmon's rehab was not coming along too well... and maybe they thought they would have Blackmon shut it down for the year, which Blackmon did not agree with.
With difference of opinions, both parties might decide to reach an injury settlement.
The thing I would like cleared up, though, is that an injury settlement pays a player for specific number of weeks that he would have spent on IR. I'm not sure whether that means Blackmon is immediately a free agent, or whether we will not be a free agent before the number of weeks he was paid to be on the IR for.
The NFL: Where Greg Jennings Happens.