Gles error in the Lord of the Flies?

I'm reading the Lord of the Flies in school and Piggy gles play a big part in the story (they use it to concentrate the sun to make fire) However isn't that like completely wrong. Piggy can't see things that are far away so he is near sighted. Don't near sighted people where diverging lens for gles. However you can't concentrate the sun with diverging lens; you need converging lens. I asked this in cl but nobody knew what I was talking about. My parents are optometrists and I'm pretty sure I'm right. Is this right?