I don’t believe that. Chinas prison stats are around 1.69mil (which is oddly on par with the US - per capita not taken into consideration). However, per the Global Slavery Index, there’s an estimated 5.8 million people enslaved there. And we know that there were over 1 million Uyghur Muslims, and we really don’t even know the extent to which that is happening either.
I’d be willing to bet that there’s a lot more slave/prison labor going over there than even we realize.