See here for a breakdown of the paper.
Adrian Zenz is polarizing, to say the least. His 2018 paper, "'Thoroughly Reforming Them Towards a Healthy Heart Attitude': China’s Political Re-Education Campaign in Xinjiang", argues that despite what were at the time consistent denials by the Chinese government (e.g. here), public bid data revealed that these were lies. So what are bids?
Bids are basically contracts posted by governments to solicit companies to provide a service or good, such as building of a certain facility or procurement of certain equipment. They're a common tool of functionally all modern governments, which, at the end of the day, are not construction or IT firms and need outside expertise to implement policy goals. Zenz gathered bids from online platforms designed to connect Chinese firms with government contracts (the US operates one such platform at https://beta.sam.gov/).
What Zenz found was that beginning in mid-2017, Xinjiang saw a massive spike in bids calling for the construction and outfitting of highly securitized detention centers all across the region. These bids were specifically labelled with terms such as 'legal system training' and 'transformation through education,' terms that have become hallmark euphemisms for the mass internment and reeducation program.
Here are some selected translations and commentary on four of the bid documents out of the 78 total cited in Zenz 2018: