All 3 are easily possible.
He had a cell phone issued by the Iranian government I’m sure. They know where he is at all times I’m sure.
Back channel and the fact the US would act are plausible
One thing would be a near-certainty SolemenI wouldn’t have a cell phone on him or near him. The NSA has shown that if you carry one they know where you are.
All three factors that I mentioned are individually possible. Taken together, they are unlikely. Since each carries a possibility of less than 50%. In the case of a pre-arranged understanding as to WHAT actions the US would take beforehand? Far, far less than 50%.