It should be "양고기" and translated as mutton or "어린 양고기" and translated as lamb. The implications of "eats sheep" is really disgusting - makes it sound like the sheep are being eaten alive or the boy is living in the wild, like "wolves eat sheep: 늑대는양을 먹다".
Isn't sheep and lamb basically the same thing?
Lamb is the young of sheep.
However, it is true that one usually eats lamb and not sheep. The latter has a stronger taste and is more expensive to raise as it takes more time before killing it.
But I guess, they choose the generic term here rather than what is maybe more commonly said in English. I don't think Korean differentiates between lamb and sheep when talking about food.