While China officially recognizes the right to worship, the government heavily censors publications with religious messaging and frowns on "open" worship. Christianity is fairly minor in China, and is probably viewed as foreign and exotic most people, similarly to how westerners view shaolin monks and buddhist temples. South Korea, on the other hand, is pretty big into Christianity.
The crackdown on muslims isn't really about Islam itself, but is really about the government wanting to maintain an ethnic hegemony. The majority of Chinese people belong a group known as han Chinese, while Chinese muslims are ethnically from the various -stans and central asia.