While I generally agree with you, as Nagasaki is a bit isolated in the southwest, surrounded by seas and inlets that make it time-consuming to travel to other parts of Kyushu, based on his proposed schedule, I don't see that he plans to visit anywhere else in Kyushu. As a tourist destination, Nagasaki has more to offer historically and culturally than Fukuoka, IMO.
Actually, you can fly to the Goto Islands from Fukuoka too. But from Nagasaki, you can both fly and take the boat.