Who rescues Noah and Abbey from their dinghy in Chapter 17? Why is this surprising to the children?

In the morning, several planes passed overhead but didn't spot the small dinghy. They were in deep water, probably fifty to sixty feet. Soon a boat was heading right at them. As it pulled closer, they could see that it was Paine and the pirate stranger. Paine helped the kids onto the boat. He turned to the pirate and introduced him to Noah and Abbey. It was Grandpa Bobby.