Could the boy swim?
Hard to say. But the article in the link above says he was from Mongolia, visiting Hawaii with his parents and 8-yr old sister, and that he had "no ocean or scuba experience." It's quite possible this was his first experience with being in the ocean; the article said the family arrived in Hawaii on Tuesday Jan 1, and the accident occurred Saturday Jan 5.
First time in the ocean + first time in scuba gear + questionable conditions = ??