smells centralization...

Nope. Just administration of the guarantee (the backing). Everything else is decentralized. The token still trades without interference from a central authority. But unlike bitcoin which has nothing backing it, Tether will have a pot of cash stashed away (with an administrator - hopefully trusted....)
That's centralisation. Requires trusting a human(s). Admin runs away with the reserves and the tokens are worthless.
How is fiat reserve proof verified in a real-time, automated fashion in a way that isnt manipulatable? Humans can intervene with the reserve indicators, no?