Being read your Miranda rights also serves as an explicit acknowledgement by the state that you have those rights. Most of the time, this isn't really important, but in this case it would have served a very important purpose.
The Bush administration systematically created a legal netherworld for people they captured on suspicion of terrorism -- people usually referred to as "enemy combatants". They weren't arrested per se, so they weren't entitled to a trial, lawyers, or even the basic rights we associate with a criminal trial such as protection against self-incrimination (i.e. the right to remain silent). On the other hand, the administration argued they weren't prisoners of war either, so the Geneva Convention didn't apply to them.
By defining enemy combatants in this negative way -- in terms of what they are not -- the Bush administration pushed enemy combatant status into a grey area where no pre-existing legal rules seemed to apply. That's how they argued that torture was legal: they said that laws prohibiting torture only applied to prisoners of war or people charged with crimes, and that because enemy combatants weren't either of those things, they could legally be tortured.
If they had read this guy his Miranda rights, the Obama administration would have made it clear that they would treat his future as a police matter and that they were rejecting the enemy combatant framework in this case. They failed to do that, and I think it's a wasted opportunity.
(By the way, when justifying drone strikes and the courtroom procedures at Guantanamo Bay, the Obama administration has continued the enemy combatant framework that Bush's lawyers established.)