Read about Byzantine Fault Tolerance here and here.
Byzantine Fault Tolerance (BFT) describes that in order to guarantee liveness and trust in a system with 3f + 1 participants, at least 2f + 1 must be have honest. Therefore at most f can be dishonest.
BFT does not apply here. So long as the majority threshold t for valid blocks is set to > 50% of the fixed validator set and less than t validators are dishonest, no subset of nodes can collect sufficienlty many attestations for a malicious block for it to be accepted by the honest nodes (the majority). Each node enforces a fully deterministic set of rules for each block and for a given period only accepts blocks that were proposed by the deterministically selected validator from the set.
The reason why we don't have to rely on BFT is that we assume a fixed set of validators, not an arbitrarily growing network of decentralized nodes. This is one of the key differences between this distributed sequencer and other decentralized sequencers.
So long as the validator threshold t is set to >50% of the size of the fixed validator set, liveness and safety should be guaranteed.