"남자아이는 양을 먹어요."
Translation:The boy eats sheep.
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.