Luke, if it's about your friend, you should ask the friend directly. It would be fun, and I'm sure the parent would enjoy sharing it with you.
Every Japanese has a reason for naming their child. I have a friend with a son named Kai, and not only did they name him after the ocean, but they had specific reasons for relating the ocean to their child.
On the other hand, I know people who'd simply name their child after their favorite stars. There is a famous movie star by the way whose name is Jo Shishido. His son is also a star whose name is Kai. Jo means "lock" in his case, and Kai means "open" in his case. It was deliberate, they say.