Might be real, hard to fully know since 1. Chinese prison system info isn't fully public and 2. Leading researchers (Adrian Zenz) don't open source their info either and avoid peer review at all costs.
Based on the public info that is available, there probably are several thousand in prison for supporting separation groups in the region. The authorities have made announcements on these while some individuals and groups have expressed these people as martyrs or heroes, primarily because it's usually part of a Muslim extremist group, Wahhabi movement, or jihad of sorts.
These people and perhaps those with close association, are often Uyghur but not always and do include Hui, Kazakh, and even Han Muslims that want to establish a caliphate in the area.
China attempts to deradicalize ppl in poverty that do not speak Chinese and are at risk areas of radicalization by offering vocational institutions, many of which are called in foreign media as the same as re-edu camps. The difference is one is voluntary and the other is not. The ones that are not, are just prisons.
Many peasants see the first as a free opportunity to learn the country's language, trade skills for better jobs, and free meals and accommodation. You can actually see these same institutions throughout the country as they're targeted for the unemployed and poor, not just Muslims or Uyghurs.
Inb4 wumao. I just live here and was curious about the prison system so went out of my way to find out the difference from both the govt and local people.