They have a small set of federated block producing nodes. This is much different than other consensus mechanisms and makes many tradeoffs on the security side to allow for fast transactions.
Look at the Mauve paper below for a better idea of what some of these tradeoffs are:
https://cdn.hackaday.io/files/10879465447136/Mauve%20Paper%20Vitalik.pdf
https://medium.com/@VitalikButerin/safety-under-dynamic-validator-sets-ef0c3bbdf9f6
https://medium.com/@VitalikButerin/minimal-slashing-conditions-20f0b500fc6c