Might be looking at the ZK Compression drama too simplistically but here's where it defers from what we've traditionally seen as rollups:

+ State is stored as calldata (found in tx logs on Solana L1) — also, DA still on L1

+ Txs and state transitions are executed directly on Solana, not a separate ledger/execution layer

+ Clients provide ZKPs to validate state changes, without needing to store all uncompressed details in accounts; instead, compressed account state goes onto Solana L1 (In zk Rollups, ZKPs are submitted to the main chain to verify the correctness of a batch of state transitions executed offchain — goes back to point 2)

In summary it seems to really come down to where execution is conducted and state is located. 

In ZK Compression, it's all on Solana.

With zk Rollups, execution and state is on an ancillary chain — it just sends periodic commitments and proofs posted to the main L1.