The origins of his name are explained in the story.
Occasionally campers would see Storm Boy wandering the beach after a storm (he loved to beachcomb at this time). Mistaking him for a lost child, they’d try to get help to rescue him, only to be told by the locals not to worry.
‘That’s Hide-Away’s little chap. He’s your boy in the storm.’
And from then on everyone called him Storm Boy.
What this snippet also implies, is that it’s more than a nickname. Storm Boy is as wild as his home!