In the article he mentions “Their goal is just to exterminate all Uighurs in one way or another”, if that is the case, why not just shoot them all? Why did they let him out?
As to the larger question, most genocides stop short of literally just shooting everyone. That doesn't mean the goal still isn't eradication of a culture.
China does care about legitimacy internationally, and simply shooting millions of people into roadside ditches would be a step too far. But this process of concentration camps under the banner of combating terrorism is enough of a fig leaf, and enough of a slow progression, it doesn't generate the same sort of immediate opposition abroad. As we see here sadly.