That's covered in the original story. This was a training mission, to get the crew up to the number of hours needed to be cleared to go on real missions. The reconnaissance systems officer (RSO) was the one listening to all the radios, not the pilot.

This seems a perfectly sensible thing for the RSO to do on a training mission, since on a real mission he might need to monitor multiple frequencies:

> I was beginning to feel a bit sorry for Walter in the back seat. There he was, with no really good view of the incredible sights before us, tasked with monitoring four different radios. This was good practice for him for when we began flying real missions, when a priority transmission from headquarters could be vital

At this point, they have passed their hours threshold and are heading back home. The pilot says:

> Just to get a sense of what Walt had to contend with, I pulled the radio toggle switches and monitored the frequencies along with him.