>Unlikely they would store such material on a system that was open to being hacked.
Any system can be hacked. That is a fact.
>I doubt Iran could hack an air-gapped system located in a secure facility.
Yes you are correct, that would be very difficult, but it could be done.
All systems phone home when a connection becomes available.
The device may be secure, but there is always the human element.
Especially if someone from inside wanted to access the data.