Rollups are L2 scaling mechanisms where transaction execution is done offchain in the rollup node or sequencer. The state is updated on the L1 based on this execution. Rollup nodes also publish transaction data “rolled up” as batches and blocks on the L1 chain.

When it comes to following the blockchain data structure of adding the reference of previous (parent) block to the next block — rollups do that.

But the representation of blocks and consensus on L2 could be different. In addition sequencers could just be centralized in some rollups.

Hence, rollups do use some characteristics of blockchains while customising some things to suit the execution on L2s.