It’s hard to fathom how you arrest 31,000 people then transport them to another country.
My rough guess here: these centers are run in towns just across the border from China. Burmese military likely rounded up entire buildings of these scam centers at gun point and drove everyone in it by truck to the border. Law enforcement in dictatorship. This also happened over 2 month period, not just in one day.
It’s the Tatmadaw aka Myanmar junta. They are a brutal authoritarian dictatorship. It’s not much different to if North Korea did it.
At the moment the Tatmadaw are facing massive disruption around the border with China as freedom fighters try to show China how the junta are losing control.
For that reason, this is likely a political stunt designed to show China they are still strong. It’s probably a lot of random citizens mixed in with actual scammers.
In body bags.